Praising children for hard work rather than "for just being smart" is about their own personal wellbeing. Kids who get called smart in their early years have trouble facing real and difficult problems later in life, because they suddenly feel "wait, I'm not really smart" and other such pathological feelings. It's about encouraging problem solving, not just blindly working hard, and teaching that problem solving is a continually evolving process and not some innate thing that you either have or don't have.
It's true that the real world doesn't recognize hard work in a consistent way, but I think this is more about personal development and wellbeing rather than implying hard work will make you successful, for some definition of successful.