Wait... you want me to bust my ass to escape the 9-5 life, so I can go work in a shared office downtown in some city every day?
Not likely...
I have clients, if I had a home office, I'd struggle to score contracts, for one thing.
Secondly - you don't have to work 9-5 in an office, or spend an age travelling to it. I always travel outside of the rush hour, and my office is at most a 5-10 min drive. I like it because it ensures I get out the house, talk to other people and get a bit of social interaction done in the day at least.
Lastly, I've met numerous people through the office that have led to good things. Good solid connections that are making me more money. Your comment about signing a 12 month lease is wrong too - I'm on a 1 month rolling contract. I can move out whenever I want.
If you're a proper introvert then I can see working from home working well, no distractions, no people, just you and your work. For me though, I need that bit of social interaction each day to stay sane. I like having a chat with the receptionists, talking to other business owners when I grab a coffee and finding out how they're progressing, etc. It's good motivation too, and has also opened up partnership opportunities for me.
If you have a wife and kids at home, the distraction thing becomes massive too. (Lots of people I know who moved into the office building I'm in moved from home offices because they couldn't take always being sent on errands by the wife, etc.)
In the end it comes down to your living situation and your personality type. An office isn't perfect for everyone, neither is working from home. Although I do think it's really important to make sure you don't work where you sleep, in terms of room, so to at least get a separate office at home if you're going to work there.
Incidentally, my reason for working for myself is the same as Kaedus.