Because we expect a junior colleague to learn from feedback and not have to fix the same problems in their output year after year.

But having learned from the feedback they or you then go off to work on something else and, unless you move onwards/upwards/both in perfect sync, and you end up with new juniors who need the feedback afresh.

Also: I've always avoided being anything like a lead or manager, but I do effectively have a couple of relative juniors ATM who I wish would have a better long-term learn/forget ratio when it comes to feedback from myself and elsewhere!