I think Stanford must have felt self conscious about its declining admit rate. Would not be surprised if it goes below 3% within 3 years. I believe they are increasing their incoming Class size every year; they got enough demand, land and money to do it unlike some colleges which might be limited by the land size.
One thing I think it’s unfair to include 4 year graduation rate when it comes to ranking (by USNWR for example) Stanford because Stanford students tend to take off time to do other stuff before graduating. When it comes to top colleges, I don’t know why this factor should be important.