You're delusional if you really believe that a game that plays exactly like Baldurs Gate 2 would be more successful than a coop friendly. I am honestly shocked that there are still CRPG devs around that to not include Coop at all in their games after the resounding success of DOS 2. Even a bad coop mod is better than having none at all. And I say this as someone who rarely plays Coop. I really would like to know if Swen actually believes that Stadia will be a success or if he just likes getting money from Google? (who doesn't?)
Where did I say it has to have no co-op mode at all?
I think @Hawke pointed out that the cash invested in creating an MP is never going to waste because after the success of DoS2 (and MP coop games in general), having a game with Coop-MP guarantees a steady amount of buyers. So they will never lose money as you said if they allocate resources to create a good MP mode, even if it costs some features due to the need to adapt the game to MP.
That I agree but do not know if that is desirable, tho.