It's not a matter of how fit the person is. Have you ever worked at sea? The North Sea? Working a fishing vessel in the Gulf of Alaska is the most dangerous job in America. A guy 275 pounds in trouble on a deck covered with ice is too heavy for OTHERS to rescue reasonably without taking excessive risks.
It is a considered limit.
Served on a submarine, I assure you it is harder to get that 275lb man out of a sub than off an oil rig. (Realistically 250 to 260 given it includes wearing work clothes.)
Big men don’t get cold nearly as fast as small men, on the other hand.
But helicopter capability is key.