I think that advertising trainers on Steam would open a can of worms that we do not need open. They would be seen as going against their own anti-cheating policy. It would also give the impression of "If you truly want discounts, you need to join another club." This would further kill the openess that is the Steam platform. Ultimately, I personally prefer to have CH just percolating in the background.
I hope this all made sense....
I never did think anyone would be banned. If you remember back to Max Payne 3, all R* did was place multiplayer cheaters in the same game sessions so they wouldn't bother non-cheaters. R* certainly didn't care about single player cheats/mods at all. I pretty much figured they'd do the same with GTA V. MP cheaters get sent to a land where everybody cheats, and single player cheaters get left alone to do what they please.
Blizzard on the other hand will never see another dime from me after banning single player trainer users from Starcraft 2: WoL. This is not the Blizzard I grew up with. The Blizzard that allowed you to install as many copies of the multiplayer portion of games like Warcraft and Starcraft for free, as you like. This is some evil doppelganger just pretending to be the real deal.