alt Hacker NewsOr it's curiosity (genuine or polite). Maybe, for some people it tips the scale into trying the app either because they were already thinking about trying some/any app, or switching away from their current one.
I don't know if anyone who's asked me has started using the app as a result, but I think it (anecdotally, again) supports an idea that a successful results for one app organically helps its name recognition.
Edit: unless you meant the difference was between people asking which app vs which spouse.
No, you understood me exactly as I meant it - which app. I met a partner of five years on the apps and people often asked how we met but they never asked which app (Tinder) - we actually saw each other on multiple apps but she did not respond on Bumble because it forced her to send the first message, which I thought was interesting feedback.