If your political tribe controls a given institution, then there is generally no need to do things by legislative fiat-- you simply do them, and your choices are status quo. Meanwhile the patrons of a library have essentially no say in who staffs their libraries or the schools where those librarians are trained, whereas the state legislature is at least theoretically democratically accountable.

Not making any kind of normative point here, just observing that it's a little less clear than "selfless librarians vs meddlesome politicians".