Sara Saperstein told me that at Reed, students who don't know what major they are often become psychology majors. Partly as a result of this, the psychology major isn't as challenging or as interesting as it should be. Sara is no longer a psychology major.
At Mudd, engineering is the (unofficial) default major. Engineering is also the most difficult major in terms of course load: it has difficult labs, 3 semesters of Clinic, and allows students only 1 free elective for their entire 4 years. I don't know why it's the default major despite being so hard.
Do other colleges have "default majors"?