Because it isn't quite the same as an individual taking a jog. That individual isn't running a business as they are jogging. They aren't creating value and making a profit from someone else so it isn't an issue.
I agree that it's just another ploy at taking money from someone else who earned it - Colorado is ever-increasing their socialist agendas these days. Regardless, hats off to Colorado for coming up with a clever excuse to tax someone else's success, lol.
Two other thoughts I have on personal trainers using free landscape for business ventures:
1) It looks bad. They appear to be free-loaders from the outside looking in. No rent. Possibly no insurance.
2) Then again, when I apply the principles of Capitalism (which is far superior to any other form of economy), I have to say that the personal trainers are adapting to a crappy, over-inflated economy that is hard to make a living in. It's brilliant, actually. They have found a sly yet very legal way to reduce costs. People like that are going to add value to our economy in years to come. So hats off to them as well.