Is there a physiological reason for why some people are natural early risers and other people the opposite?

Circadian rhythms: Yes. Circadian rhythms are different in everyone of us. It is a very complex system of mechanisms to provide restful periods to our brain, which is working all the time. Please look at the topic and learn about this very interesting topic in function of the pineal gland and hypothalamus. Thank you for the question.

Yes and no: Our sleeping patterns are determined by our habits. If you get into the habit of staying up late at night you are naturally going to not enjoy waking up early. Our body's circadian rhythms are changeable. We can accustom ourselves to sleeping in better alignment with natural day and night cycles. Fyi the same change in the circadian rhythm causing us to sleep at night, also occurs in mid afternoon.