You're right, but idTech is almost by definition that "novelty" kind of engine. And it did help id to sell more games. It's just apparently not enough.
Id made games to demo their engine. No one is going to buy an engine without any games. They don’t even sell idTech anymore. It’s used for their games which are not making any money. No game sales doesn’t support the reasoning they should keep the engine around.
For whatever reason idsoft has not been licensing their engine for a long while. AFAICT it's not that "nobody's buying", it's that "they're not selling".
Except that the obvious reason their recent games see lackluster sales is because they're on Gamepass, which precludes needing to buy the game to play it.
Yes, and those usage stats show that the overwhelming majority are playing the game without having bought it. One can't argue that these studios should be shut down for poor sales when Microsoft themselves are sabotaging the ability for these games to sell for full price.
The whole point of gamepass is that you don't buy the games. If enough people are playing it through gamepass that shows it supports the value of gamepass, if not sure that's a problem.