Massive ecosystem. Pretty much all applications and a shitload of developers in crypto are on Ethereum, and pretty much all applications on other chains are forks of what has been developed on Ethereum, which says a lot. Just look at the top 100 cryptocurrencies, how many of them are tokens on Ethereum? A majority?

Decentralization and safety. Ethereum could have lower fees by sacrificing decentralization like many other chains do, but they don't skimp on these values and in doing so they put safety first. And even if Ethereum did sacrifice decentralization it only goes so far and it is something all chains will face once users increase.

Solution to the scalability trilemma. Ethereums solution is rollups and sharding, rollups are being implemented right now and has/will drastically decrease fees, sharding will plummet them even further whenever it arrives. The future is that people don't use layer 1 on Ethereum but use the rollups on Layer 2, you can preview this by buying ETH on Crypto.com, withdrawing onto Arbitrum (still quite high fees while in beta), and use on Curve Finance, just like you would with Ethereum Layer 1 or Avalanche.