> With that kind of control, why would they share with the artist?

Its in both parties benefit to find a mutually lucrative deal. More so when the customer is not that bright and motivated by "passion" and "fan culture". That same sort of passion (about music) leads to all parties underpaying a lot of staff (people want to be in the industry for some reason). Tech has its own version of this, see game development for over worked and under paid talent who does the job out of "passion".

"Influencers" selling burgers, backpacks, sports drinks and screw drivers is no different than concert t-shirts, posters, coffins and condoms. An artist is more than just the songs they sing. It's the film / TV that work shows up in. It's the other products artists can sell (a lot of this is other peoples art but...) and the things they can promote. They can exist without TM but the same cant be said in the other direction.

And some times the artist do get screwed. When your management and TM/LN folks have a relationship that dates back to Bill Graham Presents there is likely a back side deal that gives the management an extra kick.