I don't think anyone is arguing that D&D shouldn't continue to change. Sure, there are always "edition holdouts," but most people are happy to move on to a new set of moderately altered rules every decade or so.
I can speak for myself: I have embraced every new edition change, from when 2E came out to today. I will most likely embrace 6E, whenever that comes out. I am not opposed to change, as a general rule. I'd even be open to something radically different, mechanically speaking.
But I also don't see the point of something too radical. The game works, warts and all. It is fun to play. Sure, fine-tune it, bring in new ideas with optional rules and the cycles of editions. But there is something rather iconic about the core components of the system that, even if they aren't as cleverly designed as other games, make you know you're playing D&D. Levels, Ability scores, Hit Points, Armor Class, some kind of Saving Throws, Vancian magic. That's about it.
As I said above, I much prefer Ars Magica's magic system, and I could go through the list of D&D sub-systems and find games that, I think, do them better. But I'm also happy to play D&D, as it is, in whatever D&D. It is sort of like your home town: it probably isn't the best town in the world, but is...home.
We should also consider the popular of the game right now. Realistically speaking, WotC is unlikely to depart from the basic chassis of 5E...unless the popularity complete tanks. Most people are fine with the rules as they are, and among those who aren't, most of them just change it to their liking.