As best I can tell:

1. Money. There’s a lot to be earned here, and the advertising spend to entice users is equally high.

2. We already live our lives on social media anyways. What’s one more app?

3. A very good value proposition: access more singles than a random bar, and avoid the painful uncertainty of whether or not they’re interested. (Whether or not it delivers on this is another matter).

4. MeToo. There’s basically no chance for miscommunication if both parties swiped right.

Tinder was originally Grindr, and it was meant to solve the double problem gay people had when finding a match, which is both the smaller dating pool and the risk of stigmatization. In this respect it was a huge boon to the gay community. One can imagine plenty of other such communities where such an app could be beneficial.

Grindr obviously influenced Tinder, but they were produced by different companies.