Why did he become a weekend warrior when
he could have become a full-time warrior?

Suppose you went to a recruiter and they said they didn't have any pilot
slots available. You could join the USAF and take what they have.

You could go over to the Guard outfit and find that they have some slots
available, but you have to join the Guard first.

Suppose you join the Guard as enlisted, get selected for pilot training, and
receive a commission.

Presto, you're a pilot trainee, instead of a clerk in the payroll office, or stuck
in a rocket silo in Montana.

Would you rather be a pilot, or be a PFC burning **** in Sihanoukville?