Mojang is in the difficult position where they can't make dramatic changes to the core gameplay loops of the game as it would no longer feel 'minecrafty'. Minecraft and its community has been around for so long and I am sure most players (including myself) would not be too happy to see a major change to the core gameplay loop of minecraft and for it to become a different game. Mojang also need to continuously update the game to keep Minecraft somewhat relevant. As we saw, after Mojang was bought by Microsoft and they stopped updating the game for over a year, the popularity and relevancy of Minecraft greatly declined. Minecraft needs these seemingly pointless updates to keep hold of its community by adding new and interesting aspects to Minecraft without transforming it into completely new game. This is necessary for them to keep Minecraft relevant and for us to not get bored and forget about the game.
But I mean... why would there be major changes? Why would any game drastically change in any update? In theory there could be a Minecraft 2 with significantly different gameplay. But in 99.99% of games you'd be extremely lucky to even get a bug fix after 11 years, let alone the kind of updates Minecraft is still getting, especially if you only pay for it once.
Edit: That's not to say it wouldn't be fun to get a new game mode. But no sane person would ask for a new game mode for Left 4 Dead 2 or Resident Evil 5 or Modern Warfare 2.