How do you know this? We know almost nothing about anyone or anything that happened during Roman times - the fact that a few scraps have survived is hardly an indication that most knowledge deliberately destroyed managed to escape.

Those other ways do not get rid of a potentially serious environmental contaminant. Or do you prefer if those "waste dumps" remain unused and potentially dangerous.

It both serves as a very valuable source of rare energy and at the same time gets rid of the "waste" of old redundant processes, what's not to like ?