If you cut down a few trees to build a house then 50 years later the forest will reclaim the land. If you instead cut down the entire forest then that can't happen.
>We have been using nonrenewable resources for hundreds (tens of thousands?) of years, and yet we keep finding more.
Multiple civilisations in the past have collapsed at least in part due to resource shortages. Again though, because none of these civilisations were _global_ the collapse was local and could be recovered from using outside resources.