This is a wonderful (and awful) example of engagement to a purpose.
The creators set you up by making you laugh at people. People who are just like you, doing something you probably do every day. Then your stomach drops with a couple seconds of suspenseful "Oh, no, I know where this is going," before they hit you with a shockingly graphic ending.
Humor to grab your attention and connect the story to your daily experience. A sudden tonal shift to jolt you. Final images you can't look away from, that evoke horror and terror at once. It's an incredibly powerful emotional journey.
And just to make sure it's as effective as possible, the PSA also pings on the factors that influence how we remember messages. It's repetitive, dramatic, useful to your life, and the last thing it tells you is the most important.