Thank you, Ed!
I first found some friends to play D&D with in '91 with 2nd Edition (I'd wanted to play for years but just couldn't find anyone before then) and was introduced to the 'Realms with the Purple Box, and was given a big set of 'Realms novels by a college student working at the program I attended during summers at Penn State; maybe 10 books including Pool of Radiance, Pool of Darkness, The Night Parade, Spellfire, and Elfshadow (can't remember the others) but I honestly didn't care much for the setting that I read about in the boxed set (although I totally loved Spellfire and Elfshadow.) I can't really put a finger on exactly why, but the Purple Box seemed to be too... cheery? It just gave me forced Disney vibes. But after maybe 3 years of playing D&D I was introduced to 1st Edition and the Old Grey Box, and I absolutely loved how the 'Realms was presented in that set. It just felt so much more interesting and cool. Maybe the grey color had something to do with it, but I think it had more to do with the way the original set was written with a feeling of mystery and danger, whereas the Purple Box seemed more to me like everyone was a cheery Dalelands farmer and the world was just too twee. Then the 3rd Edition book came out and I totally loved that, too. I could read about the Elves of the 'Realms forever and a day.
I won't speak of the 4th Edition changes.
Greyhawk is my personal bag, but I love the Forgotten Realms, too.