This kind of thing is so rare - the last time this happened was 40 years ago - the cost of planning for it, or retrofitting, is way too high relative to the risk. One night in 40 years. That's 1 in 14,600 compared to the A/C running maybe, 7,000 of those nights? I'm not an engineer, but this is a common problem... how much deviation do you plan for relative to your budget? We could make every house gas with a backup propane tank and a backup generator. but it would raise the cost of the house by another $50,000. Is that "worth" it for one night in 40 years? Most people would say "no" and those affected tonight will probably forget about it in a few weeks. And that ignores the added expense of buying all the propane and laying all of the gas lines, etc etc. Utilities do this kind of planning all the time.
Someone else mentioned as well that most madd built new construction homes are engineered to last through the 1-3 year warranty period and that's it. They're not going to put more money into a tract home than they have to. And most of the buyers are fine with that because they get granite counter tops and "wood" floors and that new home smell.
(Not making a judgment at all, just an economic observation about preferences)
The bottom line is that we could seriously prepare for this, but is it really worth the money or could that money be better spent relative to the rarity of the circumstances?