IMHO, it is possible that Joe was overlooked because the assistant AD wanted his son to have the job.
I really don’t think this is a fair assumption. Kyle was working full time in basketball for an organization that churns out D1 assistants like an assembly line. His path was proven and common.
Joe was working a non-basketball full time job with some AAU coaching and skills development on the side.
Taking away playing careers, nepotism, and being an alum and Kyle’s resume was much more typical of a D1 assistant than Joe. Beyond that I have no idea why Joe decided to leave his post as DBO (another typical path to becoming a full time assistant).