Ethereum is plagued with criticisms of its less than optimal scaling capabilities and high gas prices. There have been talks about increasing the scaling capacity of the Ethereum mainnet for a while now.
However, the Ethereum ecosystem needs a solution for scaling right now, and if Ethereum is not able to give these new applications a platform with enough scaling capabilities, they can seek alternatives like the BNB Chain or Cardano. Optimism rollout was created to solve exactly the scalability problem of Ethereum.