In the end, all reasons resolve to either "it's what we had at the time" or "someone thought it looked good."

Not always, for example original CD disks had capacity of 74 minutes to accommodate Beethoven's Ninth Symphony.

	▲	rasz 37 minutes ago \| parent [-]
		That one also turned out a myth :) CD size was determined by Cassette tape dimensions (diagonal, human can still hold one in one hand) and that combined with conservative pits/lands/track pitch choice drove the play time. thus CD runtime was derived from something "what we had at the time".