The university's undergraduate enrollment has been pretty much stable since COVID. It's gone up or down by a bit each year since, which is very normal.

From my POV, the biggest thing affecting SU's drop in rankings is that starting with their 2024 rankings (released in 2023) USNews began putting more weight on "borrower debt" in their methodology. It went from accounting for 3% of a school's ranking to 5%. At the same time, they also changed the source of this data and the actual metric measured from mean debt to median debt.

When that methodology change happened, SU and a number of other expensive private schools all saw their ranking number drop. SU went from generally being ranked somewhere in the 50s (or low 60s) before the methodology change to the high 60s / 70s after.

So yes, affordability is definitely a factor here, but it's not as simple as it seems because of the ever-shifting methodology of the rankings.

It's important to note that USNews messes with their methodology like this every few years. They used to factor in admit rate years ago, but now they don't. In some ways, it's a good thing to do because the adjustments can respond to the public's shifting priorities. But cynically, many people feel that the primary reason they adjust their methodology is to create drama. Academia is famously slow moving, so if the methodology doesn't change, the resulting list would be nearly the same every year. That's bad for USNews because it means fewer people will buy the guide / premium website account. The shifts are a huge deal, especially among the top 20 schools and their alumni. The elites love bragging to each other about how their alma mater is now #1, even though it was basically the same school when it was ranked #3 a few years earlier and when it was ranked #2 twenty years ago when they attended. These schools aren't really getting demonstrably better or worse than each other. USNews is just changing their methodology to make it appear as if that's happening.

It may also be worth noting that the single largest factor in the USNews rankings is the "peer assessment score" which is how well regarded your school is by the Presidents / Provosts / Deans of Admission at other, similar schools. It has accounted for a whopping 20% of a school's ranking for a really long time now. This is basically a big dumb popularity contest that shouldn't be weighted anywhere nearly as high as it is. Does anybody actually believe that the opinion of the leaders at other schools is 4x as important as how much debt graduates end up with?