I think that has more to do with the learning curve than with RxJS itself. Once you learn how to use it, it becomes an incredibly powerful tool.

Apples & oranges. Angular (web app platform) can't really be compared with jQuery (JS lib) I think. Angular had a rough, chaotic history which hurt its popularity, but if you check out the latest version I think you'd find a very mature, batteries-included framework. Especially for enterprise settings with lots of developers I find it the superior choice. It's just not the coolest kid on the block for all the indie developers.