I'm pretty sure I never saw a single half-orc PC in all my AD&D play in the 80s, across multiple groups. However, when I started playing 1E with a new group in 2004-2007, it was half-orc city. This is just one of many seeming paradigm-shifts in the conventional wisdom between the way the game was played then and the way it's played now (though admittedly this is a different group of people than I was playing with in the 80s, so it's entirely possible if I'd been playing with these guys then they'd have been playing just the same way).
I'm not sure what caused these shifts, but I've come to suspect it was the rise of D&D computer games (which led people to take a more mechanistic/optimizing look at the game to figure out what are the "best" classes, spells, magic item combos, etc.) and the internet (which allowed more fans to communicate with each other so that the conventional wisdom could become more widespread and regularized without the sort of local and regional variation that was seen in the early days of the hobby). 3E cemented this paradigm-shift by taking this new perspective into account and tailoring the game towards it, and 4E appears to be going even further in that direction by significantly redesigning the game to eliminate a lot of "problem areas" that, at least in my experience, only became problems sometime after the 80s (heal-mule clerics, 15-minute workdays, Christmas Tree Effect, scry-buff-teleport, etc. etc. -- none of that stuff ever came up in any of my 1E games in the 80s).