Memory is such a thing that we put down our car keys and later can’t remember where.
We can’t remember being in the womb. Were we there?
Forgetting one’s previous birth upon taking the next appears to be a law of nature (though a law that apparently has exceptions).
It might also be said that if we could remember our previous births, the burden of the memories would be unbearable. The memories we carry around from just one life are sometimes sorely distressing. Multiply such memories manyfold, and they would surpass our ability to deal with them.