I'm agreeing with @
JeffB too. 5e so far is, IMO the most catering toward nostalgia and taking only the most financially safe steps edition.
I think, but it could be just my personal bias, that this quote is his justification and rationalization for not making setting and lore books.
If you don't want to make anything that was done before, well, you won't make an awful lot of things. Besides, his reasoning, that "reused" material wouldn't be interesting, because people seen it before... Well, what about the new gamers, who didn't? What about them, who wasn't here for the 2e era, or even for the 3e FRCG? The material would be completely new and interesting for a LOT of people. It's just no in-line with the game's focus on new gamers, reasoning not dong books because old fans already have that material.
And what about system updates, new material, even the dreaded metaplot, because some people like living, evolving settings? DMsG material is ok, but it's old. Old as layout, old as artworks (although I like a lot of the old books' visual style) old as story, old as plot, old as system. It's not backward-compatible, and in the case of living settings, like FR, even the lore is not the same.
I generally haven't got any personal problems with Mearls. I enjoy a lot of his writings, regardless of how I like the current approach of D&D or not. I generally try to not make any personal attacks when criticizing it. But this specific quote for me is just PR talk, which wants to show in a more flattering way something, what ultimately is just "because it won't make enough money and we have to make money".