Just think about the reality of that for 1 minute. Would they as a one man band be out for that long every day 5 days a week year round? I doubt it. I never was.
Your thinking from the point of view of someone that already works for themselves. Not everyone has that mindset and theres the difference.
Suppose one of them decides tomorrow to do that. How long before their earning what I pay them now? How will they survive in the mean time and so on.
I agree to a point but think of it like this-
they are out at 7am right now to line someone else's pockets, what better motivation than to do the same and keep all the gold.
They have already gained the knowledge of pricing structure and what is achievable. They could poach your work, do it for less and still be on a real winner.
You have already motivated them to a certain degree- to work their socks off for someone else for 30k they must be motivated.
They will know just how cheap it is to set up on their own- a year of hard work is certainly worth the end result.
None of this requires anything more than a tiny bit of common sense and motivation.
You do well to keep them and I agree about the mindset, I've seen it before but it must be very tempting knowing just how much wealth they are creating and handing a huge chunk over to someone else- particularly when they see that someone else's lifestyle/fancy car etc.
With the information you have made public I'm surprised the local competition haven't destroyed you! I wouldn't dream of posting what you do.