How come there’s not an app that’s successful at helping people making friends?

I don't think an app can ever overcome the personal and cultural forces at work here. I've seen people who can make great friends over any medium imaginable, and others who remain lonely despite having every opportunity. I don't believe it's the failure of the apps, rather look to the culture to see how friendships are valued and formed.

I see my generation has no value of 'friendship'; friendship as a serious commitment which has benefits and responsibilities. People want a convenient way to not feel too lonely, without giving up an ounce of personal convenience.

I've begun to have a conversation with new people I meet at the first or second meeting, beginning with "what does friendship mean?". Then you can set your expectations at the beginning rather than setting yourself up for disappointment. This will also scare away people who don't want a commitment, so prepare for that.

Aside: I recently noted that Germans seem to have a real value of friendship. I have two german friends who check-in, and plan things on a regular basis, and clearly have a place in their brain reserved for considering how they can build their friendships, and I've heard the same anecdote often. I'm from Quebec originally, and there also saw the huge gap between anglo relationships and francophone ones (francos keep in touch).

An 'app' to make friends?

It's called going to the pub mate. Not sitting playing with your fondle slab.

Bad advice IMO. One can make friends anywhere. If anything, I'd go to an activity, convention or event that peaks your interest.

Making friends is hard. It's a big commitment for both parties, you have to dedicate quite some time to it, and find common grounds to talk and share things about. It's also harder without some task or activity that can be done together other than chatting/writing. Not to mention having the right mindset for it! I wouldn't find it surprising if it were extremely difficult to be successful at making other people become friends as an objective and focus and not a "side effect" (online videogames, communities, et cetera)

I don't know why I am replying to a throwaway account, but anyway....

I can sit in 1,000 pubs for 1,000 hours and not even talk to someone, let alone make a friend.

For some of us, it's just not that easy. The few friends I do have, I somehow acquired 20 years ago, and for some reason they've not got bored of me yet.