4# aircraft do not fly on 3# every day as well. It's also a rare event. And yes a twin will fly to the nearest suitable airport but it can be 3 hours away from the point of failure ! 3 hours on a single engine at about 18000 ft into the clouds often riquiring de ice i.o. 31000 on 3# above the clouds.
And what about a twin # aircraft crossing the pacific if you consider that a 4# aircraft have to land immediately after one engine failure ?? Do you realize 3 hours on one engine with about 300 peoples, having to descent down to 18000 ft into the clouds, requiring the only remaining engine to de ice himself and the wings !? Is that an acceptable risk taken every day by hundreds of twins ?