Who would you have maintain the land then?
Well when it's not been stripped back to a mono culture it tends to look after itself.
But I suppose we could use the £280m+of farming subsidies to pay for some to do it? We have a lot of national parks already.
Remember the issue here is farmers don't want to keep some of thier natural in exchange for the subsidies they want to use 100% of thier land for industry, sell the produce abroad and be paid by the tax payer to do it while endlessly trying to stop the public using the land. (For the sheep farmers it's fairly easy, as well the natural land is exactly what they need, I think thier complaint is the tree requirement)
For many areas i suppose a wind farm would make the land profitable, and be minimally impactful for "naturalising" the land in regards of ground and insect populations, maybe less so the birds.
But then wales is a strange Dinorwig and it's absolute monstrosity of mining waste is a unesco world heritage site rather than a "we should really clean up our mess" problem. So God knows what the real solution to our issues is.