FR was mostly presented through novels and video games, with a number of campaign guides tossed in there as well. I know that's how I was introduced to FR.
That's my point.
FR was very much a child of gaming in the 80's and 90's where material was stuff to be read, rather than stuff to be used. TSR was very much a fiction book publisher almost more than game creator. There are literally thousands (if you include novels - tens of thousands) of pages of material for FR. And, out of those thousands of pages, we've got what, a dozen or so modules? None of which are considered very good.
Contrast to Greyhawk where we have a few hundred pages of setting material and dozens and dozens of modules, many of which are iconic to D&D. Even with the resurgence of Paizohawk in the pages of Dungeon in the 3e era, we got three Adventure Paths all set in Greyhawk. Mostly thanks to [MENTION=2174]Erik Mona[/MENTION] who is a HUUUUGE Greyhawk fan.
But, that's my point. Greyhawk has always been presented as a setting to be used, rather than a setting to read about. Honestly, I think that has contributed so much to its endurance. How many old gamers like me have pulled out their battered, worn copy of some 1e Greyhawk module to use in a pinch over the years? Many I'd wager. Those modules are iconic for a reason. I've used Orlane so many times I could run the module out of my head.
Think of the most iconic locations in Greyhawk - Hommlet, Orlane, The Grand Duchy of Geoff, all the places that resonate with gamers. All locations indelibly tied to a particular set of adventures. Now, think of iconic locations in Forgotten Realms - Waterdeep, Cormyr, the Dale Lands. How many modules are tied to those locations? What adventures do you associate with them? Homebrew stuff? Sure. Tons of it. Lots of people run games in FR.
But shared experiences? Until 5e, there were precious few.