Why is Hangout a thing?

I'm not saying it's bad (because people can play SRB2 the way they want) but what is the point of this mode?

I'm genuinely thinking about it because it feels like it can be done on any IRC-like program instead of the in-game servers.

Hangout exists because not everyone can join the IRC chat room or the discord (as myself). Hangout is mostly to talk with other people about random opinions or thoughts that players have, and while you are totally right, in the fact that this could be done in a chat room, by doing it in SRB2 servers it opens more interaction with each other (literally just playing together). One thing about hangout is that there are specially built maps (hangout maps) which tend to have mechanisms and scenery that helps making the experience better.
Hangout mustn't be misunderstood as roleplay, since in hangout, you usually give your own opinions or ideas, not acted ones. However there's no rule that says that you can't roleplay and hangout at the same time.
Basically Hangout is a more interactive chat room, that has more possible activities to interact with other players rather than just typing or playing level after level in co-op. Or battle after battle.

It's more or less what it says on the tin - a place to just hang out, chill, explore hangout maps (which often have a lot of hidden nooks and crannies), and chat with others.

If people didn't care about this kind of thing vrchat wouldn't exist.

In this day and age hangout servers can feel a bit like a relic of an older time, but I totally understood them as a kid in 1.09.4a. I spent hours with my buddy Tom playing in them and sometimes even participating in RPs and stuff, but I feel like most people end up growing out of that kinda thing. I do however love playing VRChat which as Krabs pointed out above me is almost a natural evolution of the Hangout Server idea. I'd love to see SRB2 themed content in VRChat one day, maybe I'll start looking into that.