I know plenty of people who were married when they got them. I’m fairly sure that isn’t the reason, but what is?
According to my 1957 edition of the New World Dictionary, “bachelor” originaly referred to a young knight serving under another’s banner. The term gradually came to apply to a young male (preferably unmarried) who occupied a subordinate position–which holders of lower degrees certainly did in the medieval educational system.
I think it is an anglicized variant of baccalaureat, which was actually from baccalarius, according to my dictionary, used in Latin for young men. As opposed to your magister degree, or masters (teacher’s) or doctorate (doctus–learn-ed).
Or rather, from doctor (“teacher”), which comes from “docere”, to teach or explain.
“Master” comes from Latin “magister”, meaning “master , chief, head, director”.
Yup, college is very Medieval, all right! As undergrads, we’re just serfs. And, then as grad students, we’re just endentured servants! Of course, the profs are lords, or so they think… - Jinx
Shouldn’t a grad student know how to spell “indentured”? 
No, he’s referring to his partial plate, having lost his teeth due to poor diet from the long hours and low pay as a lowly grad student, hence “endentured.”