Remember he's arguig from an enlightened self-interest rather than from a communal standpoint; that is to say what is best for HIM, not Us.
That said, I really think WotC thinks it found the secret sauce with 5e. Lighter than 3e, not as big a departure as 4th. I think the goal is to make the Core 5e engine THE ongoing D&D engine. To do that, they need the 5e engine to run for a good long while. Eventually, we will get a 6e, but it's not going to be the radical departure from its predecessor that 3e and 4e were. It will be bigger than 2024, but not as radical as others. We may see stuff like unified spell lists or subclass progression then, but it will be after 15-20 years of 5e (14/24) being the default type of D&D. A whole generation will have known nothing but 5e style D&D in one form or another. Once that happens, shifting from a backwards compatible 5e update to a less compatible but still built on the same engine 6e will be easier.