Originally Posted by
similarly
You still have to pay people for their time.
Far Cry Primal used Far Cry 4's map.
Far Cry New Dawn will use Far Cry 5's map.
They will likely reuse a lot of character models and vehicles, character animations, etc. This cuts down on game design time and costs (which is why it's cheaper than FC5). But you still have to design and apply textures, terrain textures (like vegetation and water), structures (because although the church in the trailer LOOKS like FC5's church, in the 8 minutes of gameplay you can see it's not the same model). and a million other things.
It's simply not as easy as you're making it out to be.