I think @snowfairy137 is probably correct. The reality is that more and more students are applying EA, and while they tend to have higher stats, they may also find it easier to gain admittance. I compare it to schools like Purdue who use rolling admissions. Every year, students with good stats who apply early are admitted to Purdue’s First Year Engineering program, while others who apply later with equal or better stats are denied.
One other thing I saw last year was schools deferring EA applicants to the RD pool, and then asking the students to affirmatively let the school know if they were still interested before RD came out. I believe this is one way schools protect their yield numbers.
I have some sympathy for admissions teams. With students applying to more and more schools every year, it has to have become increasingly hard to project yields. The whole system is insane, and I am glad it is in our rearview mirror!