Today I've found a report by Coinmetrics (https://coinmetrics.io/the-ethereum-gas-report/) from 2021. We can see the spiking gas fee in early 2018 (by CryptoKitties) and early 2020 (the DeFi summer) and early 2021 (everything summer). That's interestingly the origin of the demand for L2s.

Btw, today, L2s are like fad, but for airdrop hunters only, because this is the vision (of many, and of mine) for this blockchain industry: every dApp will become a chain.

It's quite not possible in 2020 - 2021, "how tf can a dApp become a blockchain?", thought by us crypto vagabonds then. But then, the L2 trend comes, and it facilitates that vision, unexpectedly. Feel good understanding this, and see this.