Schools may increase or decrease their scholarships for whatever reason. Supposedly, USC used to be far more generous with NM scholarships than it is now, since it used to have a much less attractive reputation to NM-level students back then compared to now.
Non-NM scholarships may also change. For example, Alabama will no longer offer the engineering top-up scholarship for frosh with 3.5 HS GPA and 30-31 ACT (this topped up the university 2/3 tuition scholarship to full tuition for engineering majors) starting with fall 2017 frosh.