^STLRainbow didn't specify, but I took it upon myself to suspect he meant more with respect to "over decades"
Fair point on the suburban campus movement, that certainly gave major corporations an alternative to building a building in the CBD, but it seems (hopefully) the suburban campus movement is less popular now than it has been in decades.
But even during that movement I believe there still had been demand to be in a CBD, especially for, say, legal and advertising professionals. In my limited experience and knowledge, it seems Clayton has been the favored place-to-be for lawyers for decades now (yes, I understand this is a broad statement and there are plenty exceptions, I'm just speaking generally here).
Why and how this exactly happened? I don't know. I would like to know, though. In my years of digging through St. Louis related books I don't recall seeing a book on this. I think it could make for a great book though. Some of the big players, or at least some of those privy to the inside stories, might still be around.
Anyway, the clearest and simplest way to get the point across of Clayton's uprising (IMHO) would be to show various pictures I've seen and stories I've been told over the years showing/explaining the transformations of both the downtown CBD in St. Louis and downtown Clayton over the last 50 to 60 years. When I see such pictures, they usually do a pretty good job of driving the point home as to what got investment and what didn't.