Probably a question of faster maintance keeping her ready for use :-/
I forgot to add that we kept the same schedule when we owned her and at 500 hours we'd replace the engines with overhauled engines and we kept one spare overhauled engine in the hangar just in case.
I was fortunate in the fact that I had a mechanic (engineer) that loved working on the DC-3 and he nearly stopped all of the typical oil leaks. There would be periods when it would not be scheduled to fly for over a month or so and when that happened I would fly it for about an hour. We also ran the engines once a week when it had not flown for a week and no trips were scheduled.
We kept very good care of her and I still miss flying her. There was just something special about flying a DC-3.