Many ICO launch payment gateway choice ETH. any other crypto coins why not use in ico payment gateway.
Actually they are accepting other cryptocurrencies in their ICO too, such like BTC, LTC, etc.
Most of them choose ETH because their ICO token usually on the Ethereum chain, erc20 token.
It will be easy if they using smart contract to sending the token.
you're right, maybe because there are enough people who can use ERC20 now, besides that people are already used to it. the most important thing in a project is how the team develops their products. it will make the price of their products high. have ETH as a platform, I think that's because people are used to it.