Let's go back to the first principles. When you think about how Ethereum works, every single node has to perform the same kinds of computations to arrive at the exact same stage - all across the network. That's why its capacity constrains and it is expensive. One of the ways to scale is to take the computations off the main chain, perform them in such a way that the results can still be trusted, and stored on the main chain. The heavy lifting is done on what we call Layer 2.