That just kinda blithely assumes that there weren't an awful lot of people who were enjoying playing FR exactly as it was, and blithely assumes that a large proportion of the prospective 4th ed FR customer base were not, in fact, the pre-4th ed FR customer base.
I understand what they were TRYING to do with 4th ed FR. But (much like the now-legendary pre-4th-ed marketing campaign which systematically went through half of the history of D&D and told you that it wasn't fun) I think it fell into the trap of being developed in a team that was too insular, and too focused on the question 'how should FR have been done from day 1?' rather than 'how should we proceed with FR from the current point'. They wanted to blank-slate the place.
You could have made a more player-focused FR book without blowing the setting up, if you'd wanted to. That's just a matter of emphasis in the book. Less page count devoted to Elminster and co, more to villain organisations, and plot hooks, etc - 5th ed Eberron did this extremely well. Drop a few lines in there explaining how some hand-wavy pantheon metaplot thing means that the Chosen had to largely retire from active adventuring going forward, that's how i would have addressed The Elminster Problem. You didn't NEED to throw the timeline forward a century and turn the pantheon upside down. Vast amounts of the 4th ed book were devoted to deliberately, systematically making it utterly unusable for people who just wanted to keep their existing, pre-Spellplague game going, or even those who wanted to get any use whatsoever out of their old sourcebooks in the new Realms. And it's not like this wholesale lore apocalypse was even creative destruction - in most cases it was just destruction. Entire regions of the place were dropped into the sea or converted to blasted wastelands in an off-handed paragraph or sentence and not replaced with anything useful, or interesting, or gameable.
4e FR may have been a perfectly gameable setting, when viewed in complete and utter isolation from everything that went before it. But for someone who'd been playing the Realms for a while, it was about as far from it as possible. At every turn, it went out of its way to make itself incompatible with everything that had gone before. Regardless of how it was intended, there was no way whatsoever that it was ever going to be embraced by the portion of the player base who liked the Realms as they were. And if you write an FR setting book that's 'intended to be played', surely the the people who like and are playing in the existing FR are worth considering?