I've watched some here and there, but having to try to catch them when they stream has put me too much in the mind of old tv and catching shows when they air. Watching the recording afterward is maybe good for some white noise, but it's clearly not the intended experience I think.
I think most viewers can be grouped into 3 main categories (please note these are just very broad generalizations)
Category 1 viewers watch streams because they like the game that is being played, and basically treat it like watching sports. They want to watch skilled people doing skillful and impressive things. Maybe they play the game themselves, but not always. They tend to focus on categories rather than channels, and are quick to unfollow if a streamer starts playing something else, even if it's a similar genre.
Category 2 viewers watch streams because of the personality of the streamer and the vibes of the stream, and tend to have parasocial relationship. I won't say much about this category because I honestly don't understand the whole parasocial thing at all, I just know it's a Thing.
Category 3 viewers watch streams because of the streamer's community. They're focused on not just the personality of the streamer, but also the kind of environment they foster and how they interact with the viewers. I'm in this group, I'm on twitch to meet people and make some genuine connections. I've made some great friends in streams, not just with the actual streamer, but the other chatters as well - we hang out off-stream and play games, watch movies, just chat, etc. This group tends to contain a lot of smaller streamers supporting each other (in a bit of a circle-jerk, I admit)
From what I've seen, categories 1 and 2 gravitate towards larger, well-established channels, while category 3 prefer smaller streamers and will be supportive but disappointed if someone they watch becomes "big".
All of this is just my own observations hanging out on twitch and talking with other viewers and streamers, please take with a grain of salt. Also I have no idea how much of this applies to other streaming platforms like YouTube or Kick.
I think this is a pretty good summary overall. I'd like to supplement some things:
Category 1 viewers also contain people who want to vicariously live through someone else and experience their favourite game again for the first time. They tend to stick around only for a specific game, and will move on after the playthrough is over.
Category 2 also contains viewers who watch the streams as a pure entertainment product, more akin to watching a comedian. They're mostly interested in the banter the streamer provides. Many viewers of Northernlion and Jerma fit this description.