So that you can get the work done and not have to think about it when you go socialising with people you actually choose to spend time with?

"As a kid you go to school you are around people."

....and for a lot of people that was the most frustrating, difficult time of their lives that they wish to avoid reliving. Personally, I can't stand office politics, find smalltalk very distracting when it's happening around me and would much rather avoid the 1 hour commute each way.

I can't work from home in my current position, sadly, but I'd jump at the chance to do so. If I found myself feeling isolated from people, it would be much preferable to go somewhere with my laptop for lunch rather than fighting over the microwaves in the office kitchen every day.

Some people (myself very definitely included) need some regular isolation. Talking to people all day at work leaves me very poorly prepared to deal with my family when I get home. The idea that I can lock myself away and do productive stuff is awesome (although in practise, a lot of remote work isn't actually that isolating).

As a kid you go to school you are around people

School is the last place on earth I'd want to model my working environment on (although the open office advocates seem to be trying).

The greatest work week of my life, everybody else in the company was in Florida for a trade show. There was also a series of blizzards that dumped about four feet of snow over the course of the week - and virtually the entire northeast was shut down. I have never in my life gotten so much done in a week, and I don't think I spoke two words to another human being that week. It was glorious. Wish it was always like that.

If you're a highly social person, "X" will probably be months before you start to get cabin fever and feel extremely isolated. If you're more introverted, "X" may be as long as years. I believe though, it will catch up with everyone eventually.