You shouldn't look at it just in terms of how well it can utilize system resources. It allows for language level concurrent programming support which facilitate

You shouldn't look at it just in terms of how well it can utilize system resources. It allows for language level concurrent programming support which facilitates different programming styles. Some people find this style of programming 'fits' them and are attracted to these languages as a medium for expression. So while other languages can use threads and async-IO perfectly well to keep all a systems resources utilized, that is not the only point of a programming language. Programming languages are primarily a means of communication.