I can think of one scenario that is prompting Penn do to this
Consider a ** prestige conscious** student who really thinks they have a shot at HYPS but is unwilling to take the chance with SCEA. This kind of student applies ED to Penn and to Chicago. On Dec15th they get a favorable admit decision from both Penn and Chicago. They immediately turn around and decline Penn, either because their aid package is not as good as Uchicago, or more likely, because now they have an alternative high prestige school in their hand to aim higher. This student then applies RD to HYPS and some other schools like Duke or Vanderbilt that are known to give out merit aid. If this student gets in, they take that offer and decline UChicago also. If they don’t they still have a pretty solid school to go to or maybe a little more merit money from a non-Ivy school. All in all a fairly good outcome, without violating the ** letter of the ED contract** and without taking too much risk. Of course, such a student cares very little about “Fit” and is more driven by getting into the highest ranked USnews school.
Maybe Penn admissions is seeing this kind of applicant in their ED pool (specially well to do international applicants from some countries, for whom prestige is the only thing that matters) and wants to eliminate them.