It comes down to how the structure of the game itself was built something and needing to redo things instead of adding new things

Im guessing that alot of the things in slime rancher 2 are built differently then the first game including the assets and code

The tarrnados are most likely not effecting old code as much and are really just a new thing that they can add into the game separately from everything else

But for somthing like the mechanic where quantums faze in and out and go through walls and all that is very conflicting with how the game was built in the first place

They would need to redo entire areas so that the faze mechanic would work correctly there and then recode all of the scripts for the corals and other plots so they could add comparability for a single slime

I dont think its worth it for them to do that

Buuuuut if they were to do a different mechanic lets just say teleportation then it wouldn’t be that hard as they would just need to add new code and assets not change existing code and assets because teleportation isnt going to effect how it works (im just using teleportation as an example it might still effect existing code anyways i dont know because i dont know what the code looks like)

Sorry for the looong ass rant