Are these not people who are just deluding themselves that they are doing it out of love, when all they want to do is be famous?
I can only speak for myself, but as someone who streams off and on (mostly off, since I've got other things going on right now that I need to focus on), I have no particular desire to be famous. I'd rather not be famous. But it's really enjoyable to be able to share my experiences with other people. For a lot of games (most?), there's a significant amount of organic content that comes out of you, a specific person, going through a game's content and seeing it for the first time (or the second, or third, ... for games that have that kind of replay value). Having even one other person engaged with your journey, and reacting alongside you -- that's fun.
It's not the same as having friends over. You play with your friends. They're having their own experience, and you're having yours. Streamers get to have other people share that experience.
(To `moretai's downvoters: Yes, we can read their comment as an insensitive, unimaginative put-down of this group of people. But why should we? I think there's an interesting point to be discussed here, and I'm more than willing to read `moretai's comment as a genuine question.)