It is frequently policy to do this in an email signature, with the desire to use non-traditional pronouns driven (from what I saw) initially by students themselves. I'm guessing dating apps probably have check boxes or something? If so then it could be necessary or useful if wanting to be exposed or find the broadest group of people that you might click with.

99+% of the people on dating apps are not looking for the broadest group of people that they might click with. They are looking for the site to actually provide them with some filtering and selection to narrow down the possibilities to good candidates. Pronouns are provided to make a fractional percentage feel "included" (and that fraction is not the population you might be thinking of, but the smaller populations of activists in same category), and (using politics as a guide) another 50% to feel good about their virtue, though they have no intention of swiping right on anything but a guy in finance. trust fund. 6'5". blue eyes. citations: the okcupid and tinder studies of who gets swiped when all the votes and chads are counted.

Putting aside pronouns in particular and given hypotheticals were a user doesn't care one way or the other about specific pronouns as long as they know the person they swipe on is identity-compatible as a dating partner:

Wouldn't it be beneficial, prior to fine-grained filtering, to start with the widest group that meets minimally sufficient criteria? That way the end group of people who meet a very aggressive and specific filtering has more options. Sure, beyond a certain size it's too unwieldy, but each user may want to min/max for different values of wieldy(ness?).

Keep in mind I know absolutely nothing about modern dating or dating apps, and it seems things move too fast for even a person coming out of a 5+ year relationship to look at the current crop of temporary/permanent mate-finding tools and really know what they're getting into.