I think it's a matter of cost.
Setting up a full time generator backup is not a trivial expense ....especially considering that in the last 35 years this was the first time, I believe, that stations in my area were without power for more than a day or two.
If your station sold 2000 gallons a day with a 10 cent per gallon profit margin (totally guessing on the numbers) or $200/day ... would you put $15,000 - $20,000 (or more) into a system that keeps you in business for (at most) an extra day or two every few years?
Most stations ended up getting temporary generators (the $900 Home Depot variety) to power their pumps within a day or two.
To add insult to injury, they aren't allowed to raise prices when demand goes through the roof (economics 101 says, when demand goes up or supply goes down, prices rise).

If it were me, I'd never go for that deal.

100% reliable full time backup is nice...but you going to pay for that?