I think the chances are they do genuinely want longer notice periods because they think this will make their staff less attractive to rival employers, and give them a bigger window to replace staff who are leaving. My wife works in healthcare and they changed from 1 month to 2 month notice a while back because recruiting new staff was/is quite a slow process (due to having to do DBS checks, validating their professional body membership etc, and no doubt just general cumbersomeness of their recruitment process) meaning that if someone gave a month's notice, they were unable to recruit a replacement within that window.
However, I agree wholeheartedly with the OP that it isn't addressing the underlying issue of staff retention and has been handled poorly.
However, I agree wholeheartedly with the OP that it isn't addressing the underlying issue of staff retention and has been handled poorly.