The problem as I see it is that fluff players aren't as engaged in the process as tournament players are, just because they are more carefree about the game- or that's my theory, anyway.
So when a unit in the armybook goes by unused by a lot of players on the forums or in the places I play, what's a designer to do? I don't think I've ever seen someone come onto the forums and say "Hello, I really really like Hold Guardians despite them not being very good" or "I've built up an entire campaign around a band of Forge Wardens, changing them would destroy everything!".
Those players were very engaged and very vocal whenever a new edition came out and did something they didn't like, and especially during End Times
But you're right, they're not world builders, nor are they balance tweakers. I speculate that we might not see so many of them here because I doubt they have the stomach to see how the sausage is being made, where nothing is sacred and everything is subject to change if the data supports it.
On the one hand, we need the FAB to come out in order to draw these people back in. But on the other hand, any changes to the FAB, for balance reasons or otherwise, would risk driving them away again just as fast; a premature FAB that doesn't quite hit the mark could easily do more harm than good.
Sounds like another one of them Catch 22 thingies to me.