It comes down to a problem of boundaries, I think.
In a lot of workplaces casual chat about going to the beach with your partner is fine. Most people have no issue if it happens to come up in conversation that a workmate is in a same sex relationship, or for that matter is Catholic, or whatever.
I also think that in general small neutral indications aren't really seen as problematic either. If the Sikh guy wears a turban, for example.
Something like Pride/rainbow earrings should fit into that, IMO, but it doesn't so much because it's been inappropriately pushed in the workplace. So people regard it as aggressive, or that the person is likely to try and cause a problem for others.
It's also the case that this is not always going to be the same in every workplace. I have a number of gay friends who work as music teachers with kids. They are all very discrete about their sexuality in that context, which is to say, they don't ever bring it up in student related contexts at all. One of them runs a music school, and was very clear with the staff that it wasn't their place to be bringing political/social issues into the group classes with pronouns and such. Another is actually very discrete even in terms of his larger career, because he works with a very religiously diverse community. He has a very strong boundary between social life and work, though some people are both friends and colleagues. He wouldn't say this makes him oppressed, it's about respecting the people you work with. I imagine most of the people he works with know he's gay, but they also respect that boundary.
But it seems like there are a lot of people who can't negotiate these kinds of boundaries on their own. They need clear social signals, and "take your whole self to work" doesn't seem to cut it.