Now that they know these setting books are splitting up the fan base as they feared,
Assuming you mean to write "are not splitting up the fan base," I think you may be right, in the sense that the setting books they've done in the Ravnica format have all performed well in the market.
Look, I'm a fellow Forgotten Realms junkie who would love to see WotC release a new FR setting book several times a year as actual WotC products, starting with a true, Faerun-wide setting guide for 5e. But here's why I don't think it's likely we'll see anything of the kind from WotC -- perhaps ever, and certainly not soon. Let me explain my thinking.
Of the setting books they've released so far, only one out of five (or six, if you count Ac Inc) is set in the Forgotten Realms. Even taking into account Fantasy Grounds, D&D Beyond, etc., that book has sold the fewest copies of any 5e book WotC has put out. Personally, I think the reasons for this have to do with the book's release date (very early in 5e's lifespan) and the book itself (they hadn't yet "perfected" the 5e setting book formula that Ravnica and all subsequent releases have used, and many of the player options in SCAG are rather unimpressive). Still, I can easily imagine the bean counters looking at all the sales figures right now and saying "I guess setting guides sell great, so long as they're not the Forgotten Realms." And I can imagine with comparable ease the creative team saying, "Many other settings are totally ignored at present, so the Forgotten Realms gets only the adventure books -- at least until we see how the Realms movie turns out."
It's also likely they think that setting books haven't split the fan base yet. The D&D deciders at WotC are very cautious when thinking about what products work, and why. And even in the 90s, whenever TSR released a setting book (or box set) for a new setting, it tended to sell very well. But the second, third, nth setting books for a given setting (with exceptions, of course) tended to sell less and less well. They've partly addressed that problem with the "something for everyone" approach you described so well. But I'd say it's still unproved whether or not a second setting book in (say) Eberron would perform as robustly.
I also am keeping in mind the kinds of lead times these products usually have. Back when they gave the greenlight to the next year's worth of releases, they didn't really know how well the recent setting books would sell. And they probably thought that releasing three setting books in a row could be a bit of a risk. I doubt they have adopted an "open the floodgates" approach for setting books, but even if they have, they probably did so only after seeing the sales/presales for Wildemount and Theros. Personally, I'd be shocked if any of the next, say, three hardcovers turn out to be setting guides. Perhaps delighted, but also shocked.
Edit to add: In the meantime, those of us who do want more official setting content should absolutely be ordering the excellent print-on-demand products on DMsGuild, whether the Border Kingdoms book, the upcoming Exploring Eberron book written by Keith Baker, or even the less official offerings such as the Great Dale guide or the Malar deity sourcebook. It is 100% true that WotC keeps tabs on the DMsGuild's successes (and high-profile failures).