I think the OP is pointing out the consequences of over water flight that a lot of pilots do not take into account and, if they did have some appropriate training, might not take out-of-gliding-range-from-land flight so lightly especially low level.
I would say that the low number of deaths at sea due to engine failure in SEP shows some combination of the following:
1. It is VERY unlikely to happen
2. People are frightened enough of the consequences to avoid the risk
3. Pilots are sensible and prepared when they do it.
Frankly I think it's mostly 1.