You can do enable strict evaluation by default in Haskell, though. So, that must not be the reason why the language is not mainstream. More likely, network eff

You can do enable strict evaluation by default in Haskell, though. So, that must not be the reason why the language is not mainstream. More likely, network effects can explain how something makes it to the mainstream. For example having a big corporation behind the development and marketing of the language.