Just a few points on airliners.
Airliners prior to the B747 had pretty short range, so as a result less time over water and often more "back up engines" than twin airliners.
The B747 obviously had a large range so flight time over water increased and in its early days ate lots of engines, with the exception of flying through volcanic ash 4 engines seemed enough.
We now have big twins with massive range, and a change from hub the to hub model to the point to point model. The introduction of ETOPS and various extensions. All of this leading to many more flights spending more flight time over water by taking more direct routes.
So over time we have reduced the number of "back up" engines to one, and dramatically increased the the time spent flying over water.
Being a LAME I understand a bit. Having both engines on a big twin failing at the same time or within the ETOPS limit (has new name I think) is very slim. The reasons could be a number of individual or the Swiss cheese reasons such as crew, engineering, software (upgrades) contamination and commercial pressures.
What has been highlighted over the last few years is un-contained engine failures - on what I class as modern airlines. Recently we have been lucky with these failures, except the poor lady from flight SW1380.
The secondary damage from these un-contained engine failures (QF 32) is what is likely to cause both engines of a big twin to stop producing thrust. Loss of control systems, pressurisation, fuel and electrical items in certain combinations can increase the requirement of ditching.
Good thing aircraft are designed not to have un-contained engine failures.
As for the life jackets, a few visuals need to be shown on consequences of inflating them while in the cabin, the current brief has the same impact as leave your hand luggage behind.