About treasury in Kusama

I am reading the source code of the polkadot. Accoriding to the wiki doc and other posts, I found that treasury is implemented on Kusama.
learn-treasury
And the related codes are implemented in substrate.
substrate codes
But I can’t find where polkadot use these codes. For example, reject_proposal function in
paritytech/substrate/blob/master/frame/treasury/src/lib.rs

This is weird. Because the if Kusama supports the treasury, it should call these functions somewhere. Can anyone help me figure out this part of codes?

reject_proposal is a dispatchable function, meaning that users can call it from outside the chain. It does not mean that these functions are used in the logic of Polkadot, just that they are available.