Because most major trends in the crypto market have to rely on the Ethereum blockchain. From ICO to Defi, NFT, most of them are tokens and projects launched on this blockchain. With such a large number of projects, ETH will remain the top 1 altcoin for a long time.
In fact, not all dApp projects have been launched on the Ethereum blockchain. If I'm not mistaken, then the closest competitor in terms of the number of DAP projects launched is the Tron blockchain.
Nevertheless, he cannot beat the beloved Ethereum in popularity, just as Justin Sun does not try for this.