One of the reasons why the three new core rulebooks next year will not be released together is because D&D is such a juggernaut that the printers can't actually handle the size of the print runs!
Jeremy Crawford told Polygon "Our print runs are pretty darn big and printers are telling us you can’t give us these three books at the same time.” And Chris Perkins added that "The print runs we’re talking about are massive. That’s been not only true of the core books, but also Tasha’s Cauldron. It’s what we call a high-end problem."
