If we start counting all useless tokens in crypto space you will notice that most of this useless tokens are running on erc20 block chain ,many good altcoins ive came across have separate owned block chain and they are plain better, I guess the reason we have too many shit altcoins in crypto space is because of the flexibility of erc20 ,making it easy for unprofessionals to build there useless tokens.
We have some good altcoins that are running on erc20 but you will see then moving to their own block chain later on or it will be included in their roadmap about the future swap.
The reason why I like tron block chain is the ability to get rid of fake tokens running on tron blockchain if ethereum can do this it will help a lot.
My answer is too many shitcoins are based on erc20.
Lots of shitcoin on ERC20 because ethereum is the most popular network and it's also easy for people to make tokens on the ethereum network. BNB Coin is now starting to be glimpsed by many new projects and I think if later the BNB Chain becomes popular, there will also be a lot of shitcoin that will be made on the BNB Chain.