Its all about money and odd's.
Halon systems might or might not work. Everyone already complains about the cost of racing.
A trained foam brigade would be excellent at every track, it isn't feasible in the real world. Maybe tracks could get together and try to spread the costs out.
If you race you wonder about fire for awhile and play the odds that it wont happen to you. Too bad it happens, but it happens way less then it used to.
If I was ever upside in a racecar, I would want the least amount of bodywork on my car. I'd Imagine being upside down in a late model, your head is exposed little else. Even a small fire could be bad.