Being hold accountable actions I never took is the concept of karma. This life I have now is the result of all my previous karma in the buddhist view of it. But how do I know I deserve this life? What did I do to earn it? I didn't do anything, I just happened to be born in this life. It doesn't feel fair to not know why we're in these lives to begin with.

Your analogy seems great to me. I would know why I'm in that specific life and I would know how long I have here. Each life would feel like making progress and making progress would show I'm truly sorry for being a serial murderer in a past life. That should be how reincarnation works, everyone knows who they were in a past life and if it's lesson oriented how many lives they have to live. If someone knows they have 300 lifetimes then they would know all the details of what they did in the 300 lifetimes. Plus if god is truly omnipotent, then he can create things he himself hasn't even seen still making things novel while rembering past lifetimes.