Because any average joe and take apart a V12 inline or double row radial engine and fix a oil leak in 4 minutes!
Not to mention there is a huge difference between an engine with a simple oil leak and an engine with battle damage.
I was an A-10 crew chief for nine years. I thought I'd seen just about every screwed up thing on an aircraft from
FOD in an engine, blown hydraulics, bird strikes, you name it. Then we got to the first Gulf War and had aircraft with
actual battle damage.
Maintenance issues like oil leaks and battle damage are two complete different animals. Pilots
don't sit in their aircraft on the hot pad with battle damage waiting to be repaired. Battle damaged aircraft don't
see combat again in a couple of minutes or a couple of hours and usually not even in a couple of days.
And any average joe Can Refuel my plane, Replace Drop tanks and bombs, and Bullets, Both Cannon, and 50cal, in 30 seconds, 
30 seconds.. No but we could knock out a combat quick turn in less than 30 minutes with the pilot out of the aircraft and engines shut down. We could hotpad refuel and re-arm with
the pilot in the cockpit and engines running in about 15 minutes. This was fuel and bombs only. If the aircraft needed ammo then the pilot would get out
and we did the normal combat quick turn.
