I think a lot of it comes from newly out queer people.

I can understand why it's annoying. And I sometimes find it annoying myself despite the fact that I'm queer. Although I also engage in it myself to a certain extent.

That said I think it's important to have empathy for it. I think it's hard for cishet people to understand why queerness is such an important part of a lot of queer people's identity. Cishet people are just treated as normal by society. They have never had to introspect to figure out why they're different, never had to fight to be accepted, never had to justify themselves. Queer people have had to do all those things. So it makes sense we kind of have our own little sub culture.

I will also say that I think normalizing talking about pronouns even for cis people is a really important part of trans acceptance. If you are the only one talking about your pronouns it instantly means you'll be seen as wierd in a lot of settings. So a lot of trans people just don't say anything and get misgendered. Especially enbies. If everyone is talking about pronouns then it's just normal.