Working out at home is very boring.
Yeah, tell me about it. I used to try getting down to work out at home - the most I ever got done was a couple pushups. And if I turned on the radio to help work out - I started resting and listening to the music. On top of that, I'm fat, so I'd rather eat than work out at home, lol.
When you're out of shape and join a gym, you would never want to just sit there. There are inspirations everywhere -even if you're not inspired, you'll feel like an idiot doing nothing while everyone is working hard. Just my insight.