They assumed that BS followers would be a boon to their nascent gaming book. Unfortunately, they didn't consider 2 important details: BS followers, particularly 18-34, are broke-ass bros, by and large...and also that Portnoy was so toxic that too many jurisdictions would not grant it gaming licenses.
So they simply gave it away, wrote off the loss and partnered with the biggest sports content in the world to be their sports book.