Joh I never figured out why should deflowering be important.
I'm sure your historical interpretation is correct. Anecdotally, when I was in high school certainly, and even now that I'm in university, being the first to screw a girl is an ego thing, an affirmation of the guy's charm or studliness. He was able to get the girl to do something with him she had declined to do with anyone else. But I'm sure you are right, before reliable birth control guys had to be sure the child was theirs, so virginity before marriage was very important.