Because it was my parent's house. I'd basically been kicked out of college due to having no money; I had nowhere else to go. And when I originally moved it, it was only five. I didn't have a bedroom, but the den down in the basement was never really used, so I was able to get good sleep.
Shortly after that, my stepbrother and his girlfriend and their three kids needed a place to stay as well, and my stepdad couldn't say no. Despite the fact that there was hardly room for five; there wasn't room for ten, especially when one of the kids was only a year old and our house is nowhere near child friendly anymore. We haven't had a small kid since my little brother, who's now 15.
Yeah... at that point I was kicked out of the basement and had to sleep in the living room, sharing a couch with two of the three kids. It sucked.
Thankfully my sister took me in last August, and I'm now in my own apartment. Paying rent sucks sometimes but I'd rather have a room of my own. I hadn't had one for a year when I finally moved here.