Because we know that miners got huge profitted through mining all because of Ethereum higher gas fees. So if you invest for set up a ethI suggest if you choose ethereum then don't buy ethereum try to invest for ethereum mining setup.
I wouldn't follow this advice as it's insane to make the investment on the required hardware (which is fucking ridiculous in price due to scalpers right now) when ETH is moving to Proof of Stake. Sure there are mining pools but the point of crypto is decentralization not pooling everyone together.