It is by design. To prevent people from storing it. There are lots of guesses out there, and ALL ARE WRONG. I had this proven to me a few years ago when I ripped apart an old volkswagen that had been sitting for 50 years unused after being parked in a field. It sat there so long that the aluminum engine had oxidized down to white dust. Gas was still in the lines and it smelled FRESH FRESH FRESH and got cold on the hands just like perfect gas. No one seems to have the answer because the correct answer is a "conspiracy theory". I do. Gasoline has been sabotaged for 30 years. Just to stop preppers from having it. And I won't accept anyone's answer as to why it breaks down no matter how techie head they claim to be when I saw for myself perfect gas come out of the fuel lines in a half century abandoned car.
Obviously chemicals are added to modern gasoline to cause it to turn to lacquer after a short period of time, so preppers can't keep a supply on hand that is anything meaningful. It is all part of the great American knock down we are currently witnessing in another form, at the NFL.