Why did most US Universities switch to semesters I recently meet someone attended a US school still using the quarter system.
I've heard several theories, the most popular being that the semester system is easier for university to administrate.  I've also heard it is so the university breaks will line up better with K-12 school break schedule.

No one has ever explained to me why semesters or more efficient, or more family friendly.  I only know 1 person educated with the quarter system in the last 10 years.  Is there a reason most US universities adopted semesters?
There are arguments in favor of both semesters and quarters, but these seem to be inconclusive. (In the U.S.:) In fact, in the 1960s and early 1970s, many places were on semesters... but there was a fad of switching to quarters, so many switched. Then, in the 1990s, there was a fad to switch (yes, "back") to semesters.

So it does not seem to be that it was eventually discovered that semesters are better. Nor that quarters are better. Plausibly semesters are easier to administer, since there're fewer registration events per year. 
On the other hand, students seem to like the shorter "marches"...