Why would existence remove my knowledge after reicarnation?
why would nature be so cruel

"Cruel" sounds like dukkha -- as if nature were ill-willed and unkind, and we were averse to that.

So I guess that's among the many kinds of view or perception that we should overcome (in order to do away with dukkha), craving things to be other than they are -- though maybe also acknowledge whatever truth there is in it to become dispassionate about whatever is impermanent.


  "He abused me, he struck me, he overpowered me, he robbed me." Those who harbor such thoughts do not still their hatred.


to remove your memories and wisdom reincarnation

I suppose you're not supposed to see them as "your" memories and "your" wisdom.

They are memories, perhaps they are wisdom, but they are, "not mine, not me, not my self".

To some extent wisdom isn't removed -- from the world -- by death, in that the Dhamma continues to exist. I think that's similar to the view that there's a dharmakaya.