It’s only “straightforward” because you want it to be. Res ipsa loquitur doesn’t apply when you are comparing half a bag of apples to a quarter gallon of orange juice.
My wife is a graduate of one of the best Patriot League colleges and I am a graduate of one of the best UAA universities. I have great respect for those schools, but I can see when someone is blowing smoke about them too.
Try and find data to show that a graduate of Amherst or Williams with an English degree, or a history degree, or a math degree, or a chemistry degree, will earn less in his or her career than a graduate of American University or Holy Cross with an English or history or math or chemistry degree. You won’t find it, because it doesn’t exist.
Now look at placements in top graduate and professional schools - that is what so many NESCAC (and Ivy) students are shooting for. 80 percent of Amherst grads go to graduate school. The Payscale survey deliberately excludes people with degrees beyond a BA from their survey, which means that a huge percentage of students from the top NESCAC schools don’t even make it into the data.
Bottom line - colleges that are designed primarily to send students directly into the business world tend to have higher average salaries after a few years, and the methodology used by Payscale is guaranteed to oversample those young workers. A graduate of Williams or Amherst or Bowdoin or Middlebury can have that too - but a lot less of them want it.