I feel like this has been studied before, and lots of times: nature is uncontrolled. Which really leads to constant (like every 10 years or so) disasters of one kind or another (usually an invasive species), destroying plant growth and biodiversity.

Humans built systems to prevent all this from happening, 1000s of little custom ones in 1000s of different little places with 1000s of different functions and kept those systems running. Irrigation. Bringing food (and edible trash). Preventing collapses. Building dams. Removing invasive species from specific areas. Those are probably the big ones. That's why there is the continuous nature across Europe. It's entirely artificial and it's due to farms being so incredibly widespread. Just look at the map. It's absolutely incredible how far and how much there are.

The "natural" Europe is really mostly steppe dotted with swamps and forests, usually next to each other, with vast open spaces, with very few animals, in between. That should be the situation one would expect to return.