Polleke - Profile

Alright, I have read up until chaper 28 so far and I am liking it. Careful! 1 Spoiler incoming. The only reason I really have any troubles with what is going on, is that at one point there was a sudden and drastic change. But it is not really explained why he couldnt both use magic and cultivate right? Or did I read over it it? It seemed like it was a forced choice. But the reason why it was a choice, is not really explained. please someone enlighten me <3