Haha, I just replied to a similar post at bodybuilding.com...
(1) - I use a storage shed in the back yard as my "Gym" so I do actually have to "go to the gym" to work out so that satisfies the need to get out of the house or garage and go to a facility to lift.
(2) - It is away from anyone else that is running around the house that would be a distraction. No one else is in the "Shed" unless they are there for the same reason, and that gives you any motivation that you get from being with like minded people with the same goals.
(3) - I get to pick the music.
(4) - I get to set the volume level of the music.
(5) - I decide what equipment is installed.
(6) - I decide the operating hours.
(7) - No waiting on equipment.
(8) - It is close to home.
(9) - I don't get any feelings of intimidation from larger builders laughing at my small build.
(10) - I dont have to pack my own, or buy prepared from the gym, my post workout nutrition.
(11) - The annual cost of membership is very low.
(12) - No "Personal Trainers" constantly bugging me to buy their services.
(13) - I also get to set the temperature in the gym myself.
(14) - No one is mis-using or abusing the equipment and tearing it up.
(15) - The equipment lasts longer because of less use by only one or two people.
(16) - You have to include the New Years Resolution rush argument.
(17) - no one looks at me funny if I want to grunt, yell, or scream while lifting heavy.
(18) - If I drop or throw a weight it's ok because IT'S MINE!