What keeps a lot of maintenance firms in business is the fact that there are very few hangars available in which you could put your plane and get a freelance engineer to work on it.
Most hangars are owned by somebody who either runs a maintenance business, or is a mate of somebody who does, and they make sure you don't do any work indoors.
I have been doing my own 50hr checks, occassionally with a freelance A&P/IA when some extra work needs doing, but we have to pick a reasonably non-horrid weather day, and in the winter this means hats, gloves, thermals, the works. It's easier to schedule it with an N-reg because the 50hr check doesn't have to be done on any precise timing, but nobody is going to do an Annual that way because one normally does Annuals during the winter and working outdoors for a week is simply not on; anyway one cannot put a plane on jacks when it's windy, etc.
It's an occassionally depressing manifestation of the ancient rule that property owners rule the roost.