I've heard that companies stopped putting spares in some vehicles for a couple of reasons, one being due to how wheels have become much larger and wider, that actually storing the tire in the trunk after you've changed the flat is a problem (I can't verify the truth of this, but I can think of some vehicles where this is the case. However with the proliferation of SUVs this is not an issue - although weight of these huge wheels could prevent some less-robust people from being able to lift them into the vehicle), another being weight reduction - the CAFE regulations under Obama were so high that companies were looking everywhere for ways to reduce weight so they could meet their CAFE requirements.

My new car didn't come with a spare tire, just one of those repair kits and a compressor.  However, I was able to buy a 'spare tire kit' to retrofit my car with a standard spare tire, jack, etc.  After the vehicle is sold to the customer, adding a spare tire doesn't affect CAFE ratings...