Maybe I don’t understand you correctly, but Binance and BSC are working their own blockchain. Indeed, BSC is a hard fork of the Go Ethereum (Geth) protocol. That’s why BSC and Ethereum Mainnet have a lot of similarities. But BSC developers changed Geth protocol significantly and made another mechanism with cheaper and faster transactions. You can read more about this on Binance.com if you are interested (https://academy.binance.com/en/articles/binance-smart-chain-vs-ethereum-what-s-the-difference). Everything was made very clever and provides cross-chain interoperability.