All of these are great reasons. In my humble opinion it can be summed up in only lack of sales. There are a few reasons for this:
1. People that want to buy american buy their son or daughter a 17,000 mustang instead of a more expensive camaro. They save money on 1) initial cost 2) insurance 3) accidents. A new driving should not be in a new firebird/camaro. Face it, they are too damn fast. Mom and dad want their kids to be safe.

People that don't care the origin of the car buy their children imports. They get good gas mileage, have low insurance rates, and a high resale value. What's bad about it?

Kids that buy their own cars now are influenced by movies like the fast and the furious, and they think imports are race cars. For some reason they see their ground-scraping body kits, air bags, ph4t stereos, and "bling bling" rims as cool. I'll never understand why. My own father said he would contribute to buy me a new honda civic, but I wouldn't be seen in one of those damn things so I paid for an older camaro by myself. I'm sure the opposite case is true for a lot of kids nowadays.