I don't want to defend not wearing one because I always wear mine. But according to movies, you just pass out. You either wake-up at the hospital recovering, at an island with the most beautiful or handsome person or a pet that loves you, at the home or head quarters of the evil person who will tell you their plans or on a boat that rescued you or on a floating piece of drift wood. Definitely not totally bloated and half dissolved. No, that never happens.

You need a type 1 lifejacket to help prevent drowning due to unconsciousness. Type 2 will also turn some people face up.
These aren't commonly used for general boating and watersports as they restrict movement.
But type 3 could at least keep you at the surface where hopefully someone close by sees you and gets your air holes out if the liquid.

Not only that, but often sudden cold water temperatures will cause you to inhale.