It really is amazing. Now every medium-sized city has at least one "Guitar Center" type-store with 300+ guitars hanging on the walls. When I first started playing in the early 1980s, you'd have to go to a "music store" which sold everything from trumpets to pianos and had maybe a dozen guitars in stock.
I don't know the exact numbers but between 1958-1960 Gibson made roughly 1700 Les Paul Standards ('bursts). At the time, they couldn't give them away. Now Gibson probably makes several hundred Les Pauls a month --if not more, and they sell every last one of them. Not to mention the countless other manufacturers.
I’ve always thought the very early years of the Fender (then) Broadcaster vs. the Gibson LP were remarkable in a quaint way. With Fender you had this radio guy (Leo Fender) making a guitar where of all things, the body was screwed to the neck! Huh? He’d take the things out to little country bars in Southern CA and let the guitar players try them and probably tweak them this way and that in response to their comments...not there’s much to tweak on a Broadcaster/Tele in the first place...he did this more with the amps...and in the end he ended up with just a marvel of sheer primitive functionality. I recall the first times I saw Fenders (having grown up on Martins) how cheesy I thought they were. Really, it would be hard to get more primitive than a Tele and still have a functioning guitar.
Meanwhile, Gibson had what was (with the sole exception of the solid body) a pretty traditionally built guitar...set neck, real finish, inlays, binding, carved top...but they undoubtedly distributed the things through their traditional dealer network at the time and as you say, they didn’t exactly jump off the racks. Maybe it was because “Gibson” players were looking for those f-holes in an electric, maybe it was because So CA, wild place that it was, didn’t have such an established tradition. Just kind of interesting how the two developed.
It’s still quite remarkable to me (as I’m sure it is to most) how utterly right Leo got it with those original designs, the Broadcaster and the P-bass.