Comment by lentil_soup

It's just a lot of work.

You need to build the engine/tech, need to support various platforms including building a rendering pipeline (so Vulkan, DirectX and Metal). You need to support animation (probably just 2D?), audio (including various effects and params), different types of input, a UI system, etc. To author the assets you need editors of some form for building the scenes, for cinematics, for the narrative, for the animations, a lot of these will be custom. Then to get the assets in the game you need a pipeline that coverts everything into platform specific formats. And all of this has to be performant, targeting 60fps ideally and cross platform.

That's just the tech side. Then you need all the other disciplines to be in sync. Can't start on animations until you have characters, can't start on those until you have concepts but can't have those until you have a narrative. And these will go via a lot of iterations as you try things out and figure out what works.

Then there's testing, the possibilities from a user perspective are really broad so the bug surface is massive. For a simple app the user is quite limited so it's simpler to enforce rules and unit tests. With a game a user can do a lot across many platforms and the issues can be on the low level graphics driver or just logic puzzle errors.

Then you have certification, platform holders have a book of tests they do to your game so you don't brick the console. Things like, does you game handle unplugging the console while you're saving to disk?

I can imagine they'll reuse a ton of tech from previous games, but there's always new things you need to do. Two years is actually pretty fast for the industry.