However, some times the circumstances that gave rise to the fence are gone! You still need to do the work to show that this is true, or at least some best effort. But if after a cursory check there is no compelling reason, retorting "ah but there may still be some use, go search the wisdom of the ancients further" is a terrible response. That is how you calcify debt and become unable to adapt to changing circumstances.
There is a balance between preserving out of an abundance of caution and tearing it all down because it was inconvenient or "new is better."
We already have plenty of innate status quo bias. We don't need to heap more on top without good reason.