Why don’t we just reprocess the fuel into new fuel?
Oh, yeah. Politics.
Bingo. In fact the US is unique in that we don’t reprocess our spent fuel by statute. The annual amount of actual hot isotopes that can’t be used for anything would fit inside a thimble, and the great bulk of actual non-fuel rod “nuclear waste” disposed of in places like WIPP are contaminated nuclear facility clothing like smocks and gloves, and hospital radiological wastes.