Successful, pleasant dungeon run? Added to friends.

All dating sites have effectively two sets of users: people who use it until they get a long-term partner (A), and people who can use it forever because they are unlikely or unwilling to get a long-term partner (B). That is effectively intrinsic to the activity they are born to serve (dating). This said, there are enough people belonging to the B set to keep them in business pretty much forever.

There is also the option to provide ramps for people in A towards some other form of socialization (double dates? dinner parties?), but I don't think anyone really tried it yet.

Well, that's only true when you consider matchmaking for short interactions, which surely prevents community bonding. Longer interactions do not prevent bonding.

As for Tinder... I'm pretty sure you can find the equivalent of "dedicated servers" where to form a community, but I don't think that's what most people would want.