Selling books is not where the big money is at. Movies, streamed series, toys, video games. The big bet is that the game just helps launch an entertainment multimedia bonanza.Never underestimate how stupid humans can get when they're motivated by greed. To a Hasbro exec revoking the OGL might seem like a magic button to bring all those 3PP dollars home to WotC.
I wouldn't be surprised if management was sold on the idea of 5E keeping the franchise alive long enough to launch other media but then it's success took everyone by surprise.
The TTRPG market is chump change compared to movie and video game money.