See... I had more time to think about the question 'SHOULD the game evolve'...
People often mistakenly consider evolution as being a thing a species does to get 'better', or that evolution is a constant progression. Truth of the matter is that evolution is about adapting to your environment. It's not the 'strong' who survive, it's those that are the best suited for their current condition, and if those conditions change they either adapt or die.
In the case of D&D, or any product of its kind, if it doesn't adapt to changes in its environment then it will 'die' by losing too many customers.
And here's the thing... people change ALL the time. I'm not the same person I was 10 years ago, 8 years ago or not even 5 years ago. My tastes change, my opinions can change, and I'm not alone... In other words, this mass of people's opinions, of ever changing people's ever changing opinion, IS D&D's environement.
If the game doesn't evolve and just keeps pumping out Adventures that you can solve with the same ol' skills and same ol' spells on the same ol' classes or the same ol' characters... Well maybe you'll have people who will be content with this, and that's fine... but there's also a large portion of the player base that'll get bored. They'll get bored of the classes they've been playing for 10 years+ and want to try something different... And if D&D no longer has anything different (For exemple, if you're into mundane characters, D&D has a VERY Limited range of options. Out of the PHB alone there is the Berzerker, the Champion, the Battlemaster, the Thief and the Assassin who don't have supernatural powers, wth Berzerker (and Open Hand Monks) being very borderline. You'll run out of those options fast) people are just going to go elsewhere.
Maybe that stable core will attract new players to replace the ones who leave... but will that be enough? Is that a risk WotC is willing to take?
A commercial product is like a living animal, and the more it engages people in complex ways, the way D&D does, the more evolutionary pressure there is to keep evolving because the 'environment' is constantly in flux. Even Monopoly comes out with new versions from time to time, even if the classic is always on shelves.