Running, especially distance training (and not just a quick jog on the treadmill), is primarily a higher socioeconomic activity simply because it is a macro version of the marshmallow test. I really hate to say this because I am a bleeding heart empath, but people who are willing to endure prolonged discomfort for the sake of fitness and/or competition at a later date tend to be more motivated than those who decide to forgo the discomfort for the sake of immediate pleasure found in a case of beer, some video games, or whatever else is easy and unproductive. This kind of personality trait tends to bleed into other parts of life.
This is not to say that all runners are highly successful and productive - Lord knows I have had some running buddies who are total "morans" - but there is a strong correlation. I have had periods of my life when the only way to get in my run was to roll out of bed at 4:30 in the morning. It sucked, but it made class and the following worknight (2nd shift) seem a lot easier in comparison.