pack colors, the 3.1 rule question

the concept of older colors being grandfathered in is something i don't get. if this change is for readability and was put into place because pack names were unreadable, shouldn't all things that are unreadable be changed? in theory it makes sense to let older packs abide by previous rules, but i don't think that illegibility is something that is justified as a holdover because it directly impacts everyone reading.

if those are justified in remaining lower contrast there's no reason that new packs aren't also justified in being lower contrast. unless there's something i'm missing here.