Because home might be an even worse place to concentrate in than open-space office. I know it is for me, it's the only reason I actually come to work instead of doing it remotely (which costs me additional 2h/day of commute time).
The people who share my home do not respect my workspace. If you think interruptions for work-related questions are productivity killers, imagine being asked to empty the trash for the fourth time in one day. Oh yes, let me interrupt this work that requires some level of concentration and skill to do something menial and distracting. Again. Or be pestered about it incessantly until I do it.
I'd gladly work remotely, but not from home. No way. If there are no small-business-incubator businesses nearby, I'll be working public library hours, thank you very much.
Well, if they hire me at local Google office, I could cut it down to ~40min / day ;).
Anyway, as my commute is walk+tram+bus+walk, I do offset this time by reading books and replying to e-mails while in transit. I'd be really, really angry if I had to spend this time driving a car.
