Why can tokens be deposited and withdrawn over more than one network?

Why can tokens be deposited and withdrawn over more than one network?
One type of asset can circulate over different chains; however, it cannot transfer between those chains. Take Tether (USDT) for example. USDT can circulate over the following networks: Omni, ERC20, and TRC20. But USDT cannot transfer between those networks, for example, USDT on the ERC20 chain cannot be transferred to the TRC20 chain and vice versa. Please make sure you select the right network for deposits and withdrawals to avoid any potential settlement issues.

What’s the difference between deposits and withdrawals over various networks?
The main differences are that the transaction fees and transaction speeds differ based on the individual network’s status.