The question is asked, a question that we can answer:
George HW Bush: What makes a one-term president?
Losing the election and not being re-elected would seem to cover it.
As to why, which is the real question being posed, PJ O’Rourke put it best. George HW Bush would have had to be found naked in bed with with a dead business recession to lose re-election. He was and he did.