Temporary scarcity of sheet film options are probably an indicator of excess demand
which the limited coating lines of Kodak simply can't keep up with, rather than diminishing interest. The sheet film base has to be periodically coated in large volume, then cut down to its respective sizes for sale. Their coating lines also have to do other kinds of film, so they can't just do any type at any time they wish. Therefore, Ektachrome sheet film will always be a feast or famine scenario, especially with 8X10, 11X14, and 5X7, which now seem to be pooled order special cuts. But the same cycles are happening with their color neg sheet films too.
Affordability, increased mfg costs, tariff nonsense, etc. is a secondary but important issue. Cost-wise, 4X5 has become the new 8x10. Therefore, the firms which choose to stock significant amounts of sheet film have to buy it in large periodic quantities, not just a convenience box or two here and there, like a small camera shop might. That ties up quite a bit of capital. Such bulk purchases have to be done strategically, at the right time.
I spent decades as a professional buyer in different kinds of product lines than photographic, but where it was either buy smart and in well-timed volumes, or else risk going out of business over the long run. Places like B&H can't dabble in this or that;
they have to commit.