i would be surprised if the majority of gameplay in Minecraft is unmodded vanilla survival still. At one point it was obviously, but at this point most players are young kids on bedrock edition using ipads and consoles. These players are going onto the sponsored/featured uber-servers filled with mini-games and lobbies and micro-transactions. They go on to play parkour, or amogus, or bedwars, or whathaveyou.

For these players new updates bring, at best, a couple new blocks to the palette of the pre-made worlds or a new feature enabling another game variant. At worst, it brings down the servers they like to play on for updates and maintenance. Huge gameplay updates would be detrimental to this playerbase, Mojang is obviously wary of changing up much of anything and breaking this eco-system.