You need to understand the main coin of the blockchain.

Within each network there is a coin that is used to pay transaction fees. So, if we send ETH to its original Ethereum network, we can safely use the blockchain and pay fees with this main token.

But if ETH is sent to the Binance Smart Chain network, then we will not be able to perform any operations, because we simply will not have the main token of this network to pay commissions.