In my experience of selling D&D for... 6 core revisions of 4 editions (with a 7th on the way!) I can say that this is the only edition where I still have a significant number of customers who buy every book that they publish. This has NEVER been the case before, as they've always ALWAYS burnt-out even the most hard-core buyer with the pace (and quality) of books. Now, not all 5e books have been the best, and I suspect that they're close to a breaking point with the new increase in price-point and the higher-end slipcases for the same (or less) content. I think the breaking point is close. BUT, it's never lasted 10 years before. I don't think that it's lasted more than three years before.
There's gotta be something to the release schedule - it's not just the advent of Critical Role and Stranger Things. Those things are responsible for the stellar "Long Tail" of people who pick up a book here, a book there, but the sustained sales across the board? That's on the release schedule.