Why developers did not resort to the development of their own blockchain and decided to limit themselves to the standard ERC-20 marker? It is much better to have your own individual blockchain than to take ready-made models.
Firstly , it requires a very significant cash costs, and secondly, much more time for development. Why complicate your life if the Ethereum blockchain fits here as well as possible.
Today, almost every project uses the Ethereum blockchain. I don't think this can last long . A month and a half ago i saw the news that the Ethereum creator Vitalik Buterin plans to introduce a lease for the use of its blockchain on other platforms.