Because BNB was also born from Ethereum smart contracts in the past so in terms of smart contracts, Ethereum still can't be matched by others, even though Ethereum can lose in terms of fees, because if Ethereum can be cheaper in terms of fees, then who will use BSC at this time ?
Main advantage of Binance Smart Chain is the fee and that's right, many people moving to Binance Smart Chain because they can't get the burden paying so much money just for the fee but after fee of ETH reduced sometimes ago, people still using BSC maybe a lot of people are now used to using BSC and consider ETH as alternative only.
If both ETH and BSC have good projects like NFT in it then there is no use thinking which is better, because both can also be good.