To keep people using the app, they need to believe (hope) that it will solve their problem, be it friends of dating. Every time a dating app leads to a marriage, they just lost 2 users. If a friend app leads to a friend group forming that no longer needs the app to get together, they could lose users at an even faster rate.

The goal for these apps then becomes, how do we give people enough hope that they don't quit the app out of frustration and hopelessness, without making it good enough to lose them as a user from succeeding at the stated goal of the app.

The marketing of Hinge played with this idea a bit, "the app designed to be deleted"... but of course, Hinge is now owned by The Match Group, who owns most of the dating apps, so it's not designed to be deleted, at least not anymore, it's designed to sell hope.