Thinking about it, and I’d like to forward the idea that prejudice against single people (aromantics, asexuals, and also just… anyone who does not have a romantic partner) follows dynamics less like anti-queer bigotry and more akin to anti-fat bigotry.
Fatness, like singlehood, is seen at large as a state of failure. Everybody is supposed to want to be [thin / partnered], and if you are not, that is a personal failure on your part, and you are pathetic and mock-worthy. The popular idea is that of course everybody wants to be [thin / partnered], and everybody is striving towards the goal, and anybody who is not [thin / partnered] is either temporarily inconvenienced on their way to correctness, or has something fundamentally wrong with them. And because [fatness / singlehood] is something that is treated as fixable, if you have not fixed it, then there is something wrong with you—and thus discriminating against you is acceptable, because your [fatness / singlehood] is based on your own bad choices.
The world is, in some cases quite literally, not built for fat or single people. If you are fat or single, the world is much more difficult or expensive to live in, because it is structurally designed for the assumption that you are thin or that you have a partner. The normative Person, after all, is thin and romantically partnered. If you are not thin or not romantically partnered, there is something fundamentally less human about you.
[Fatness / singlehood] is something embarrassing, something worth mocking others over, something that reflects your fundamental unworthiness. Every fictional hero is thin, every fictional happy ending ends with romance. Everyone in your life is either quietly or not-so-quietly worried about you.
And all this is fine and acceptable. Because in the general perception, [fatness / singlehood] is not a real axis of bigotry. It’s a choice! You could just become a different person and stop being [fat / single]! You deserve the mockery, the derision, the attempts to fix you, the world not accommodating you, because you could just become a better person and stop being [fat / single] at any point. So it’s your own fault people treat you badly, really.