Streamers aren't meant to be consumed by watching them every day for hours on end. I mean, I'm sure there are core fans who do that, probably students and single young professionals like you say, but my use case for Twitch is "hey, I have 10-20 minutes free; not even enough time for a full DotA game, but I can see which pro players happen to be online now and watch them play for a bit". This gives me (somewhat surprisingly) lots of the same satisfaction that playing games used to give me; plus it's a lot less stressful (I was mostly into competitive multiplayer games) and without any practice required to get good at the game.
Meanwhile I wonder how people have time to finish entire seasons of TV shows on netflix, given the modern trend of story-driven shows that assume you've actually seen all the previous episodes instead of pre-internet-era sitcoms that you could jump in and watch any 30-minute episode with little context. Twitch is more of a return to old-school TV in that regard.