But thousands, if not millions of people commute to work every single day.
Come on. Thousands, if not millions? They say that the number of people in Manhattan alone increases by a million during the day. More importantly, though, this has absolutely nothing to do with the 8 hour workday.
You still need to travel from wherever you live to wherever you do your work; the only way to solve this is to move those places closer together (maybe even to the same place).
In fact, I’m willing to bet that most people aren’t doing anything for 40% of the working week.
Assuming that this is true, there are a variety of alternate hypotheses. For example, this problem is pretty much exclusive to knowledge workers. Perhaps knowledge workers need "breaks" just as physical laborers do, but because the culture discourages it, they invent their own "breaks".
Today, human creativity is at an all time high because less and less people are working in offices.
This is self-contradictory: either human creativity is at an all-time high, or it's reduced by working in offices. After all, there was a time when nobody worked in offices. I'd wager that the proportion of humans who work in offices is actually increasing, even if you only look at Western cultures. Of course, I'd hardly say that human creativity is at an all-time high either (even for Western cultures alone, that was during the Renaissance).