I think it is mostly a matter of perception, based on a couple factors. For one, the increase in yearly books from 3 (2015-17) to 4 (2018-20) to 5 (2021), and potentially 6 or more eventually. The only really "Realms-dominant" period was 2014-15, with the single adventure of '14 being a two-parter in the Realms, and then all three books in 2015 set in the Realms.
Since 2016, only one year had more than a single Realms book, that being the two Waterdeep books in 2018. But then the book count went up 4 and then 5 this year. So while there's still one Realms book this year, it accounts for 20% of product, compared to 25-50%, depending on the year. But again, not really fewer books than most years.
Anyhow, I've speculated that they're going to be spreading their wings a bit, especially once more of the classic settings come out. It might be really hard to do Planescape, Dark Sun and Dragonlance without some further support, unless the "new format" for these are some kind of mega box sets or slip-cases with multiple volumes.
But I don't think they're going to abandon the Realms anytime soon. In fact, I think it will continue to be "homebase," even as they diversify D&D into other worlds and types of stories. My guess is that we'll still see one Realms product each year, mostly an adventure, but maybe eventually a setting book (in 2024?).
And again, we're going to be getting at least 5 books a year going forward, possibly more. If there are six books, only one for the Realms, that's 16.7% of books set in the Realms--half the percentage of 2016-17, but the same amount of books.
