The word 'bachelor' comes ultimately from the Latin 'baccalaris', which related to a subdivision of land. The person to whom it belonged probably worked for a larger land-owner...a kind of share-cropper, it would seem. In 13th century England, the word meant a junior knight, not old enough or rich enough to fly his own banner. Notice the 'subordinate' concept yet again. By the 14th century, it had come to be applied to a first university degree, again to indicate that the holder had not yet attained a Master's position/degree. Basically, then, the word has just meant 'junior' for centuries.
(Incidentally, it was not applied to an unmarried man until later than its application to the first degree. Chaucer was actually the first recorded writer to use the word in both senses.)