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.
It is true, ETH will not easily collapse and be displaced by others, because many project developers are using the platform from ETH to create new tokens, from here everyone can see that ETH enthusiasts are very smart and big people.
The decentralized exchanges and the like of Uniswap really help ethereum gaining a lot of projects to make ERC20 token therefore if ETH collapse means those project collapsing also which not realistic at this point since many of them has huge market cap.
Ethereum is like having its own safety net by grabbing all these projects altogether bringing traffic to ETH network it's actually very resilient.