I hear what your saying but it just doesn't happen. There are lots of cleaners that employ. There's a very big difference between going to work, going home and forgetting it and getting paid, compared to working for yourself or running a business. Most just don't have it in them. I also now pay around the 25-27k mark which is good money for the stress free job they can forget after 5pm. No admin, no expenses, no messing from customers, no vehicle maintenance and the list goes on as you well know. Enforcing a contract is easy if you bother to get a proper contract. Otherwise why would any business have one if they don't work.
I worked as an advertising sales manager for the daily mail. I ran a team of 6 people which hit annual sales of about 2million pounds. I personally sold about a quarter of that. Did I leave and set up my own agency expecting to pay myself 500k a year? No I didn't. My point is lots of jobs in lots of industries have their staff generating large numbers that they can see. Doesn't mean they all run off and set up on their own.