Chieftains and Partenavia's can fly home with only one going, and both have in fact done so.
Some pilots can't or won't.
In a well known outfit I flew with, the city based chief pilot would never fly a piston engined aeroplane. We had to do that.
Even twin turbine powered aircraft and twin jet airliners have been known to crash after an engine failure. And most accidents are caused by people, not machines.
Sure, as Tinpis says, a piston twin with only one going has lost 50% of it's power, and about 80% of it's climbing ability. But that's usually enough to get home if you do it right. Steep turns and tight circuits are not appropriate.