Comment The reason there's a market: (Score 1, Interesting) 94
Older air conditioners. Over the years, they've kept changing the allowed refrigerant in air conditioners, each one requiring a completely incompatible system. Need your AC serviced.... Oooooh, sorry, you need the whole system tossed out and replaced with an entirely new one because the refrigerant can't be obtained any more. (Happened to us twice in our San Jose home.)
This isn't to say there wasn't good reason for the change. But it's sure have been nice if they just changed it once.