Pujya Niruma offers three reasons why people are unable to remember previous lives: the pain suffered at death, the unconscious period prior to the next birth, and the pain endured during the next life's birthing process.
To learn more:
In English: https://www.dadabhagwan.org/path-to-happiness/spiritual-science/science-of-death/
In Gujarati: https://www.dadabhagwan.in/path-to-happiness/spiritual-science/science-of-death/
In Hindi: https://hindi.dadabhagwan.org/path-to-happiness/spiritual-science/science-of-death/