There is though a workforce of gardeners employed by local governments and individuals that you would be displacing. Perhaps from a good job onto the work programme.
I do not see it would happen on a large scale. Those work-to-benefit could work on things, that local government cannot afford or are not planning to do. Even cleaning wild areas which are a serious problem in some parts of woods for example. Or cleaning beaches, or planting trees in remote areas. There are those things that simply are hard to achieve when you are tight on a budget already.
No, this would be in addition to that. Often the employed gardeners have maintenance schedules meaning they have limited time in each area. I know there are countless areas near me, my commute and my office that would benefit from a bit of extra attention.