What Larry said! They play the odds and rely on the homeowner's lack of thoroughness. My experience is that even though many homeowners ask if we are insured, they never check it. Even many of the commercial accounts do not ask for certificates of insurance before we begin work.
We too have never had to submit a claim, other than one bogus claim from an unscrupulous commercial client (who by the way we will be seeing in court shortly!). Not that we haven't broken a light fixture, or blown an outside thermometer of the window, but have always made the client aware of it and fixed or paid for replacement.
The lack of diligence on the client's part is somewhat to blame. As long as there are clients out there that will not demand proof of insurance, you will have uninsured contractors out there. Especially in an unregulated profession such as pressure washing. Personally, we market our company by differentiation and have always upheld the highest level of professionalism in approach, appearance, workmanship, etc. This has allowed us to demand higher rates and distinguish us from the "splash & dashers". The clients that want "cheap work", get "cheap work".
I would like to see our state enforce a proof of insurance regulation for ANY registered businesses. If they required all businesses to submit proof on a regular basis, this could minimize non-insured business and possibly reduce our premium burdens. However, it would not stop unregistered businesses from operating.
We'll keep doing what we're doing and hope the general public gets smarter.