Earlier quoted context omitted.
Isn't the whole lightning network for bitcoin also L2?
It's L2, but you can have different types of L2s. With lightning network, you're opening and closing channels with a counterparty using on-chain transactions, so each channel can be tied back to an on-chain transaction. Before someone points out that it would require tons of on-chain transactions to onboard everyone onto it, you can batch thousands of channel open/closes into a single transaction with new protocol up…
Simply put - it can't scale to that kind of throughput for a combination of cultural and technical reasons.