This guy hit the nail on the head. Fuel economy averages need to improve. One of the easiest ways to improve fuel economy is make cars lighter. Even a cookie spare tire weighs 15 or 20lbs. A jack and tire iron weighs another 10 to 20lbs. Easily 40lbs, if not 50lbs, saved by not having to equip every car with one. Also creates more trunk space so car companies to squeeze out another cubic ft or 3 when adversing their cars to their competitors.
Ever wonder why the batteries that come in cars, especially compact cars, are smaller and don't have as many cells (cold cranking amps) as years ago? To save weight. These smaller batteries are probably 10 to 15lbs lighter than the old school batteries. Do they last as long? Nope, but the car company doesn't car since your not likely to buy a replacement battery from them anyways in 5 years or 10 years even if you had a full size battery to start with.
Primary reason for no spare tire is to save weight which helps a car company increase their corporate fuel economy averages. Secondary reason is for increasing interior capacity. Third reason is for design/styling considerations and being able to equip the car with different size/diameter tires front and rear.
