Since you wrote streamers, rather than content creators, I will assume you're referring to watching live streamed gameplay. Thus we can ignore video/clip content, such as build guides, in-depth boss mechanics showcases etc.
The TL;DR is that I'm not watching livestreamed content.
If you imagine the average gameplay session, assuming you've reached monoliths, becomes mostly just grinding monoliths. Something that, given how "stale" monoliths are right now, becomes very boring to watch. Crafting in LE is pretty quick, and once you know what kind of item you want, it will be relatively little compared to the regular mono gameplay; a similar case with bossing.
If we focus on the last question, What would make watching streamers more enjoyable? I look at the clips that are posted to the subreddit (And the PoE subreddit) and most of them end up being 'high-stakes moments'. What makes a moment high-stakes? Death/Character deletion being on the line always ...