Because contracts can call other contracts in the same transaction if they are on the same chain. This is what is known as "composition", and it's very handy fo

Because contracts can call other contracts in the same transaction if they are on the same chain. This is what is known as "composition", and it's very handy for building powerful apps on existing proven primitives (such as aggregators, decentralized exchanges, lending protocols). Also, once you launch a contract on Ethereum, it's accessible to millions who already have an Ethereum wallet with ETH loaded. On-boarding to a new chain would be more of an uphill battle. If you're worried about tx fees, there are already plenty of L2 solutions available and more coming online soon!