I think because the bots are so easy they had no choice.
Even if the bots are super easy, what is the harm in people playing against them and progressing at this stage of the game cycle? I understood (but was annoyed) when they severely limited progression early on in the game release, but now it just feels like they refuse to give in and change a decision they made 3 years ago. (For those that don't remember, they had full xp and progression in the modes against AI during the early release, then took it away without announcing it. Plenty of us were mad because we bought the game specifically because there was full progression and immediately it was taken away.)
