I think they didn't do that, because they for some reason, can't. As in, I think that the moment a patch goes live the achievements added in said patch become finalized and static. I think the same also applies to other areas such as the Relic (can't program the game to require less books, NQ items, less materia, etc) an Quest (related to the above with Zodiac needing HQ items) maybe also trade in for items sincdieing how the HQ item for the first 2 Master tome sets and the Anima items still need HQ items (time will tell on that).
Point is, SE is unable to nerf achievements for some reason
