Every time skydiving comes into a conversation, I'll say something like, "That violates my basic rule, not to get out of a perfectly good airplane until it's on the ground and stopped." Invariably, someone else says, "But they're not perfectly good airplanes!" That sure seems to be what I've observed, is that skydiving airplanes are often flying junk heaps, where maintenance is an after-thought. Additionally, even if reasonably well maintained, they are put through a lot of tough use: full power climbs to altitude, then no power descents, all done as quickly as possible to minimize the transit time. None of that's very good on engines.
Cary