It's important to remember—when talking about what an encumbrance the covers are to both string changing and stylistic approach—that during the era of their widespread use ... neither of those things changed for years with most (if not all) players.
Even though Rotosound introduced roundwounds to the world in the early-'60s ... flats were still it. Many basses existed from Ike to Ford with the same set mounted. And even though the Ox, Larry, Rocco and a few others had helped create new forms of expression on the instrument from the mid-'60s to early-'70s—and Jaco blew everyone's minds when he OWNED '76—there was no way to study their technique and equipment in minute detail at that point. Hell, now we can see how our bass heroes trim their fingernails in 1080p slo-mo on youtube.
So, as my old music store boos used to say: if the covers came mounted, most people left them mounted. If they came loose in the case, most of them stayed in the case. Likely still the same today with reissues and the like ...