Assuming this is a serious question (which, given that it's you asking, might not be accurate), it's because bimbos are generally too happy/fun-loving and not self-reflective enough (especially regarding downsides to being a bimbo) to think that it's a good idea to get debimbofied. Amma's a perfect example:
She says this like the possibility of reversing the Treatment has never occurred to her (or anyone else who's ever gotten Treated). While she does attempt to justify this assertion by listing some things that aren't included in other bimbofication drugs, the way other bimbos in the game - including bimbo!Steele - act makes me think they would similarly justify why they don't want to get debimbofied (or, for particularly low-functioning bimbos, try but fail to properly articulate it).
Bros aren't given enough characterisation to definitively say all that for them, but since I view them as the masculine counterpart to bimbos I assume the same holds true.
If it's not a serious question, disregard the above answer.
Definitely a possibility, but the consent issue I raised in the second paragraph of my comment still holds.