I's not that simple. Look at New England. Initially de-populated and left to grow over thanks to western agriculture then intentionally key that way by environmental policy. It's not inching toward anything resembling pre-colombian forests. It's turning into an impenetrable thicket. But hey, plenty of food for the asian long horned beetles and gypsy moths so that's a win. /s

There's a lot of bits of biodiversity you don't get without humans putting their thumb on the scale and forcing a different equilibrium.