Maxperson
Morkus from Orkus
You are grossly overestimating the complexity of playstyles. These are not anywhere near on par with A Brief History of Time or a PhD thesis.You realise that there is a lot of overlap between these categories? The people designing games are the same people who you find debating them on forums. I could ask for a show of hands, but I know some prefer to remain anonymous. They don't have any more special insight than you or I have.
In the same way that I could write a popular sequel to A Brief History of Time simply because I'm an Astrophysicist and educator! Again: WotC employs ordinary people, without superpowers.
That's because there is a history of lumping vastly different things in the same box, in the same way that Dune and Star Wars are both space operas featuring desert planets.
Most of what has been written on playstyles is vastly misleading, and written in a prejudicial, "outsider's view" style.
Gygax had it right from the start - present the game as a series of suggestions and ideas, and players will interpret them in whatever way seems natural to them. The only mechanical help people need is to be encouraged to do whatever seems right to them.
It's simplicity itself to get designers who specialize in the major playstyles to do the work. No need for someone who doesn't know much about one to write it up.