tf2 has a much more casual scene and is much more casual than dota 2
a 7 year old idiot can play tf2 and not get flamed, with dota im not so sure. the mechanics of dota and it as a whole are also much less accessible
star, jerma, shibby etc. being popular is just the way tf2 is, since tf2 is very casual and competitive aspects of the game are not really visible in game or in a form a pub player can see
that was a bit of a rant
im just saying tf2 is casual/pub-oriented so entertainment is going to be popular, not high skilled content