It's brave to admit that you do not know how most sequels work.They are built directly on top of their predecessors; as is Mario Maker 2. They can't just reuse existing Wii U engines and content forever...
EXACTLY! They can't pull that trick again. There is only so much left in the Wii U cupboard left to raid; and once that and the current crop of 3rd party support dries up... It's back to the Wii U era desert again...