We don't have any hard numbers on how many people are left on their marketing team (during the 50th anniversary! during new corebooks being rolled out!) but it's less than it was when they were just rolling out, say, Tasha's Cauldron of Everything.
I suspect, under normal circumstances, there would be a more distributed load and as one book is being previewed, the previews for the next books are already in the hopper (especially the time-intensive video previews they love doing nowadays). With fewer staff members, I suspect everyone's got more work on their shoulders and there may even be some skill gaps at the moment.
I do expect the DMG to get some (possibly frantic, last-minute) previews, but probably not as many as the PHB did, although there's a smaller market for it, so that's probably OK.