We don't talk about Pun-Pun
It doesn't matter what WotC thinks, sadly. As a publicly traded company, it comes down to the shareholders. Who want more money.* So WotC probably won't, no. Why bother ensuring the future of the game by helping DM's when you could sell us a movie, tie-in video games, and plush Mimic toys?Here's the thing:
I, personally, would love some DM books. But considering the overwhelming number of GM advice blogs and videos out there, would WotC think it's worthwhile to put out their own version, especially since it's practically memetic that nobody reads the DMG?
*EDIT: I'm not calling them greedy, mind. If you invest in something, naturally you want a return on that investment. But the things that give you more money in the short run might not be what's best for the product in the long term.