For me it’s nice to have someone playing the same game as I am while I’m playing, the streams are usually long so I don’t need to worry about stopping to find something new to put on and I learn stuff about the game I might have missed or just never knew. I live alone so, depending on the streamer, the conversation is also nice to have around.
I can’t say I’m one of those that only watches a stream though, I need to be doing something other than just watching lol