I mean it makes a lot of sense if they realized D4 would take more time and pushed to get DI on PC. And really from what we've gathered, D4 had its concept completely scrapped at least twice, including when it came to art style. So much of what they were working on before 2018 is probably completely unusable.
As for Overwatch, the game is supported by the fans of the characters (be it normal shippers or the other kind) more than the gameplay. I still think that if they manage to push a single player story campaign out for that, they will strike gold. But doing it up to the visual standard of the game is probably a tall order.