The systems that execute the code for and track the values of stablecoins are themselves networks that only work because of consensus systems designed around a

The systems that execute the code for and track the values of stablecoins are themselves networks that only work because of consensus systems designed around a cryptocurrency incentive. So if you want to be able to send some large amount of USDC you need some small amount of ETH or MATIC or AVAX or whatever to pay for the usage of the shared ledger, and that's where these cryptocurrencies then get their underlying value.