Astral Plane/Death/Reincarnation

I've been reading a lot up on Astral projection & the astral plane. I understand we are technically living in the 4th-5th dimension spiritually, but consciously we cannot access it without a lot of practice. But what I don't get...when we die we to go the astral plane in an astral body and we choose to be reincarnated. Why do we choose to be reincarnated back on Earth? If the astral plane is so nice I mean, why do we want to come back and loose our access/memory to it.

I've heard that Earth is more like a college for our spirits, but what exactly do we have to learn on Earth that wouldn't be taught to us in the astral plane. And ascending to higher planes.