Scummy thing for the publisher to do, but I have to say much of the blame still falls on Beamdog. Nobody wants another digital distribution platform that has no reason to exist, and the first thing the community wants from a new game is that it either runs standalone with unobtrusive/no DRM or runs on Steam. If you're worried about Steam taking a cut, go standalone. If you want to compete with Steam, BG:EE sure as hell isn't the blockbuster to launch your service out of obscurity. I seriously doubt that Atari wanted the game to be a Beamdog exclusive in the first place, and forcing the issue led to them getting screwed. It's not that Beamdog is all that obtrusive, it's just that the inevitable Steam version is now poorly supported and cuts out the developers.
My guess is that Baldur's Gate 3 was intended to be the flagship that Beamdog would ride on, but in reality they have only crippled their own development studio by saddling it with their DD platform. The cold, hard truth is that Steam takes a big cut because their service is worth it, and nobody wants a second copy. Origin is the closest thing to a competitor they have, and I've never seen a product so universally unwanted.