Partly it's down to what economists call scarcity value.
If you were the only WFP operator in your town you would charge a hefty premium to clean the taller buildings your competitors could not reach. In time new guys would come along and take some of this work, driving down prices, and you would have to lower some prices or lose your work.
This is precisely what has happened to me, I was one of the first with WFP round here and now... :
This illustrates that we shouldn't spend too much time boasting about our earnings
There aren't enough suppliers in the WFP business, that may be because it's not a mature market yet. So at present they have scarcity on their side.
But in time more manufacturers will come along and prices will fall.
In the meantime the suppliers will make hay while the sun shines, and I for one can't blame them.
I'm sure they will deny this, but of course if were that terrible being a supplier, they would find another way to earn a living....