Because, simplisticly, you probably only get to do the 10 minute journey twice a fortnight but you have to do the 40 minute journey 10 times in that same period. So it's 140mins vs 410mins; you in theory save 3h30m per fortnight by living closer to work.
It's actually choosing not to orient your life around work that causes the decision to live closer, thus saving commuting time and overall spending less time on work related activity.
It's actually choosing not to orient your life around work that causes the decision to live closer, thus saving commuting time and overall spending less time on work related activity.