Why is that a ridiculous hypothetical, but "omg they'll decrypt everyone's phones" isn't?

Because one comes from Hollywood-style make believe, and the other comes straight from the government's spokespeople?

It's happened to power plants and hospitals. You might want to recalibrate your idea of what is realistic and what is hyperbolic.

Cryptolocker attacks have very little to do ideologically with encryption; it's a side show to the main event, the fact that networks are vulnerable to infiltration. Those attacks could happen with or without encryption in the malware, but could be reduced in frequency and severity by using strong systems with strong encryption on the victims' side.

The airplane bit is where the scenario goes completely off the rails wrt encryption's involvement, but again, using encryption and strong security on the airplane's systems would reduce or eliminate the risk.