Hey! Congratulations on your acceptances! I would assume you don’t have a highly uncommon prospective major and no great hooks on your application. Your ECs, as people have mentioned earlier, are mediocre, but it depends on your recommendations and essays as to how they depict any ambitious changes you could have brought or how involved you were or how many people you influenced or how many people you touched and took your ideas to or maybe if you completely transformed and expanded the scope of things you took up. Sometimes, impressive looking stuff on CVs are impostures and great work on humble stuff turns out to be more promising. Application reading is subjective and thorough. Readers are experienced, and it is tough to agree when you think you accomplished a lot, but they really know their thing! It is mostly about diversity and good fits. They make good choices for the colleges they represent. At least most of the time.
But, also, under normal circumstances, you might see this
Yale - Reject
Brown - Waitlist
Cornell - Waitlist
No matter what happens, you already have Williams! Don’t bother thinking too much! My decisions have been real disappointing as of now 
Good luck!
Please, chance me back!
http://talk.collegeconfidential.com/what-my-chances/1970884-predict-my-results-will-chance-back.html#latest