When I'm trying to extrapolate the worldbuilding of a story, there's one big thing I like to keep in mind:
Would it put constraints on what kinds of stories can be told?
I'm always trying to maximize the amount of stories that can exist without coming in conflict with each other. This is the number one reason I don't think of Peridot as asexual / aromantic. Does it make sense for her character? Yeah, I think so - without getting into too many details, she reminds me of myself and some of my aromantic friends. Would it make sense thematically? It absolutely would: sure, fusion is not always a metaphor for romantic relationships, but if you want a metaphor for how it feels to be aromantic in an LGBT+ space, what better than a character who doesn't fuse when almost everyone else does?
But the fact is, there's nothing in the show that comes out and says that Peridot is ace, and I have to believe that's a deliberate move by the show's crew, just like how there's nothing that says gems can't identify as male or use he/him pronouns (even though none of the ones in the show do). They don't want to stop people from feeling included in the show's world.
And, ultimately, Peridot is probably the show's most shipped character. At this point, if someone comes out and says she's for-sure aromantic, they'd be cutting out Amethyst/Peridot and Lapis/Peridot from the world of possibilities, which in some ways cuts fans of those ships out from the rest of the fandom.
(As a side note, I was afraid that they would go down this route with Stevonnie's pronouns - I can attest that a fusion of a boy and a girl using "they" isn't as obvious as you think if it comes at a time when there are no nonbinary people in your life, and it doesn't really work as representation if you don't make it clear.)
As another example: The Federation in Star Trek is... incredibly vague. Is it a federal state like Switzerland? Something like the European Union? Is it a loose organization like the UN that everyone should theoretically be able to join? Point is, they don't usually tell us what Federation civilian life is like outside of Starfleet, which forces people to extrapolate.
And there's a good reason for this. The Federation is an ideal future for humanity; readers and viewers presume it to be in the right unless it's really obvious they're making a mistake. Saying that one side of a contentious real-world issue has "won" doesn't convince anyone of anything - it just excludes people on the other side from seeing themselves in your story. Either they're the villains, or they don't exist at all (which is fine, if that's what you want). But by making characters people care about, and making them believe the things you do, you can still advocate your side of an issue by demonstrating its effects on them, while offering a way for people who you don't see eye-to-eye with to still accept your story into their personal headcanon - to enjoy it, and see it as something that happened somewhere in this world, without necessarily accepting the bearing its themes have on the real world.
This is also the reason I'm not fond of fix-it fics in general. When you cut out entire movies / shows from the canon, you're not just cutting out the things that happened in those movies / shows - you're stopping readers who do enjoy those movies / shows from considering your story part of their own headcanon. If I'm reading a Star Trek fic where the author is deliberately excluding, say, Picard, that means my stories - which do acknowledge it - can't exist in the same world as theirs. And this may just be me, but I can't enjoy fanfiction unless the potential for collaboration and compatibility is there.
Would it put constraints on what kinds of stories can be told?
I'm always trying to maximize the amount of stories that can exist without coming in conflict with each other. This is the number one reason I don't think of Peridot as asexual / aromantic. Does it make sense for her character? Yeah, I think so - without getting into too many details, she reminds me of myself and some of my aromantic friends. Would it make sense thematically? It absolutely would: sure, fusion is not always a metaphor for romantic relationships, but if you want a metaphor for how it feels to be aromantic in an LGBT+ space, what better than a character who doesn't fuse when almost everyone else does?
But the fact is, there's nothing in the show that comes out and says that Peridot is ace, and I have to believe that's a deliberate move by the show's crew, just like how there's nothing that says gems can't identify as male or use he/him pronouns (even though none of the ones in the show do). They don't want to stop people from feeling included in the show's world.
And, ultimately, Peridot is probably the show's most shipped character. At this point, if someone comes out and says she's for-sure aromantic, they'd be cutting out Amethyst/Peridot and Lapis/Peridot from the world of possibilities, which in some ways cuts fans of those ships out from the rest of the fandom.
(As a side note, I was afraid that they would go down this route with Stevonnie's pronouns - I can attest that a fusion of a boy and a girl using "they" isn't as obvious as you think if it comes at a time when there are no nonbinary people in your life, and it doesn't really work as representation if you don't make it clear.)
As another example: The Federation in Star Trek is... incredibly vague. Is it a federal state like Switzerland? Something like the European Union? Is it a loose organization like the UN that everyone should theoretically be able to join? Point is, they don't usually tell us what Federation civilian life is like outside of Starfleet, which forces people to extrapolate.
And there's a good reason for this. The Federation is an ideal future for humanity; readers and viewers presume it to be in the right unless it's really obvious they're making a mistake. Saying that one side of a contentious real-world issue has "won" doesn't convince anyone of anything - it just excludes people on the other side from seeing themselves in your story. Either they're the villains, or they don't exist at all (which is fine, if that's what you want). But by making characters people care about, and making them believe the things you do, you can still advocate your side of an issue by demonstrating its effects on them, while offering a way for people who you don't see eye-to-eye with to still accept your story into their personal headcanon - to enjoy it, and see it as something that happened somewhere in this world, without necessarily accepting the bearing its themes have on the real world.
This is also the reason I'm not fond of fix-it fics in general. When you cut out entire movies / shows from the canon, you're not just cutting out the things that happened in those movies / shows - you're stopping readers who do enjoy those movies / shows from considering your story part of their own headcanon. If I'm reading a Star Trek fic where the author is deliberately excluding, say, Picard, that means my stories - which do acknowledge it - can't exist in the same world as theirs. And this may just be me, but I can't enjoy fanfiction unless the potential for collaboration and compatibility is there.