FR was popular from the outset. and was high magic from the outset (look at the old gold box video games). Krynn leaned heavily into player character exceptionalism. Magic is rare - apart from the PCs, and the baddies. There were some people trying to play Greyhawk as a low magic setting, but that depended on player character exceptionalism too. A ton of high level wizards came from Gygax's own campaign.
"Core D&D used to be low magic" is simply not true. It's always been readily available, at least so far at the PCs are concerned. What Eberron did is try to remove player character exceptionalism, by saying "what if the whole world had access to the same magic that the PCs do".
Runequest was kind of the low magic fantasy RPG in the 80s, although that did have PC ducks. And it explains why other RPGs took the high magic route. Pretty much all PCs in Runequest were Conan clones (even the ducks). All they could do was hit each other with swords. They didn't have many choices as to what they could do with a fight (you could target specific body parts), and one PC was pretty much the same as another.