It depends a lot on what specific aspect of media you're in but this isn't necessarily true. In video there's a lot of Avid, Davinci Resolve and RED, in photography (particularly fashion and very high end) there's Capture One Pro, in music there's ProTools and the like.

Adobe competes everywhere and overall it's very successful but there are a lot of niches where it doesn't dominate.

Just about everything is available on PC as well though so your point still stands. The main exception is Final Cut Pro, which is very popular with video folks.

Final Cut Pro is Mac-only