It really doesn't do much good in the natural world to be able to run at a steady pace over long distances. Being able to bolt quickly to avoid danger, however, is a more adaptive behavior, in evolutionary terms. Being capable of running very fast for a quarter mile is a more valuable ability it seems, than being able to run at cruising speed for a mile, or two, or three.
Now, the argument there is, "But in today's world, it's not necessarily advantageous to be the strongest or fastest anymore." While that is becoming more and more true, there are still advantages. For instance, running from the cops, running from a bear or someone with a weapon, etc. A good 400m runner probably has a better chance of getting away than a good marathoner. Plus, while women are starting to become less interested in men's physical size and strength, and more interested in their mind, creativity, earning power, child rearing abilities, etc....many still go after the strong man. Which is why sprinters get more booty on average than scrawny, nerdy distance runners.
In conclusion, sprinters are real runners, not distance runners.