Is it really that people are simply horribly afraid of their flammability?
An external butane leak would be about as harmful as a leaking cig lighter.
Internal leak? A perfect mixture of butane and air the size of fridge would certainly take out a wall, maybe an entire house if it knocks out a load bearing wall.
The worst part about the internal explosion is its almost certain to happen when the owner is standing right in front and opens the door and the light kicks on along with maybe anti-frost heaters or whatever else is in there.
I have seen some ideas proposed such as using the "smart" in a smart fridge for good not evil and locking the door if the system pressure drops below "X". Much more likely the "smart" in a smart fridge will never be permitted to be used for anything other than advertising and marketing, which is sad.
Energy content of hydrocarbons is about the same (to one sig fig or less LOL) and just one gram of gasoline can blow a piston rod clean thru an engine block under perfectly bad conditions (already shattered bearings, etc) so a couple hundred grams under worst possible case in a confined sealed fridge could take out a house, most likely.
(Edited to add: I have a better analogy: A perfect stochiometric mix of air and diesel the size of my coffee cup can blow the engine head clean off a diesel engine, IIRC that's how one of the brothers who invented the Diesel engine died in a lab accident a century ago. And that was just a little coffee cup sized engine cylinder. So imagine a sealed container the size of a fridge instead of a coffee cup... that'll take out a house for sure... neighbors will "probably" live but I wouldn't bet on it...)
Having some way to ventilate the gas (so you don't just get "a box full of flammable gas" situation on slow leak) without reducing performance too much might help also
And methane has the convenience property of being less dense than air. I’m not sure, but I expect that the heavier hydrocarbon gasses might be more likely to accumulate indoors.
I'm a little fuzzy about the later, pretty sure about the former, and most people don't have the privilege of living in Texas (not sure if I'm kidding or not?), but it demonstrates the safety issue that ammonia cooling needs about a hundred times as much ventilation as a normal kitchen. And insert the usual quotes about building codes being written in blood so they aren't demanding a hundred times the ventilation just for fun.
Building codes have only recently (and incompletely) been revised to allow mildly flammable refrigerants (A2L) inside most buildings for space conditioning. Amending these for A3 refrigerants is an uphill battle.
Ammonia is mildly flammable, toxic, and electrically conductive. Good luck finding/building a hermetically sealed compressor that is anywhere near affordable.
CO2 in a refrigeration cycle goes transcritical at even moderately warm temperatures, making the system very inefficient without adding several (typically expensive) changes to the cycle. Manufacturers would struggle to build a CO2 air conditioner that meets minimum efficiency standards at anywhere near current equipment costs.