Maybe the builders don't trust the client on getting paid/changing the job half way through/trying to get it on the cheap/taking the piss etc.....
Most I know in the building game are honest, reliable etc and have plenty of work but turn down jobs through lack of trust. The amount of times I've read on here " do you know a good cheap.... no such thing as good and cheap.... If you want a good job pay the money or do it yourself or get messed about.