Yeah, Jazz is heavy on theory too. Especially for improvisation and jamming, you really really need to know what you are doing and which tone will match what the group is doing at the same time.
But to play folk or rock music for example, you do not need that much of it. If you can read music sheet, you can reproduce the song. You can kinda create similar own going by intuition. But, creating the stuff Bach was creating absolutely does require tons of knowledge.
Youtube has really opened my eyes on the subject as well: there are truckloads of jazz players discussing musical theory.
Which makes a lot of sense in hindsight: properly deconstructing and playing with structures is difficult if you don’t deeply understand those structures. But I’m not really musically inclined and I’ve never been fond of jazz so I never saw this.