Can’t speak for whoever did, but for the irony, I imagine. And possibly in hopes that, if just people knowing you used the app seems invasive, then maybe users would reflect on the ethics of some of the far more invasive information published in it. Plus, more benignly, they may want men to be able to learn if a girl they’re talking to is on the app so they can make an informed decision to stay away & leave her alone. Anyone on tea oughta sympathize with that last one at least.