I know it's probably for checking how many you have but still

wait how do you get gyroids?

There are two ways

You can go to an island with kappn

Or

Dig stuff up after it rains and there will be a chance that you find a gyroid

So that if you sell a gyroid you can buy it back, if you can’t buy it then it’s just a place to keep track of what gyroids you have

I have never sold a gyroid and it always says not for sale

Then it’s just to keep track on what you have

And with fossils!

Yeah