I asked a psychonaut "Why can't we remember before we were born unless life is some sort of test?"

And he said;

"As someone who has studied brain anatomy and neuroscience: Memories are formed and stored in the brain and you don't have one to form memories with until you are born and have developed for a while. Your thoughts and memories can be corresponded to the flow and interaction of chemicals in your neurons. It makes sense that memories from this life would only be tied to the neurons that exist in your current form. If you ever lived a past life, the memories of it left with the brain/body that was left in the ground."

"To be fair, I think that on some level we do "remember" our past lives. Think about how we got here. We passed on knowledge to others and they continued to do the same in the name of progress and discovery. Think about all the tiny interactions those long gone did. Every interaction between them caused the universe to play out to how it is right now. Memory is just how we interpret the actions that came before. Our thoughts are usually words or feelings, and those are passed from person to person over time (and even person to animal). We're still passing those thoughts and feelings around to one another. The love and hate that is passed around came from somewhere, usually those older than us. But where does it stop? When did it start? Fun stuff to think about."

Another one said;

"you also can't remember what happened when you died in your last life. this is the immense power of maya which covers your consciousness and makes you forget your past lives. just think if you could remember all your past lives, and all the traumas you experienced. you wouldn't be able to handle all of that, and you'd crack."