Can I replace "part of" with "one of" here? What is the difference between "one of" and "part of"?
Yes, in this context you can replace "part of the reason for this" with "one of the reasons for this". However, these two expressions are not always interchangeable. "Part of the reason" is usually used when there is one reason for something happening, and someone is explaining part of this one reason. "One of the reasons" is used when there are multiple reasons for something occurring and they can be listed. In this case, however, he uses "part of the reason" to have the same meaning as "one of the reasons" since he gives multiple reasons.