There are two more factors in this: the first is that being unable to debimbofy Kiro after her quest is complete is what gives the quest its sense of urgency; remove that, and you detract from the player's investment in the plot. The second is that the game's writers generally don't want to write debimbofication (partly because of its ramifications on the setting as a whole but mostly because they either like bimbos or don't want to touch bimbo content at all); that conversation has already been had several times in regards to Mitzi, and it won't change for Kiro.
Besides, if you really want to debimbofy Kiro, you can always use save editing. I've already posted the steps required for the process at least twice on this forum, and I don't really want to do so again; you can use the search function if you want to find those steps.