When you have a difficult or monotonous occupation, sometimes you have to get a little creative to keep things from getting boring. Then again, sometimes that creativity can create more headaches.
Like, for example, when your one job is to kill a bunch of teenagers on an airplane and you accidentally set off a chain reaction of death and destruction that forces you to spend an entire franchise worth of movies killing kids.
In my mind, the version of Death that appears in the Final Destination series of films is one of many, like a big, morbid corporation. He's just trying to make his quota and this one kid gets a vision and screws everything up. Is it too much to ask that these kids just die like they're supposed to? Apparently.
Of course, he doesn't make things easy on himself after the fact. Rather than just go the easy route and just send an assassin after them, or create some circumstance to stick them all in a bus or something, this Death is determined to come up with new and creative ways to pick them off one by one.
Why go for a car accident or an epidemic when you could have one get set on fire, trip on a crack in the sidewalk or get crushed to death under a plate glass window? It's not enough just to kill them all in order. He's got to kill them all in the worst way possible just because they ruined his original plans.
Spite is a powerful motivator for creativity and general badassery. Just ask Death and his Rube Goldberg machinations. Or me on a particularly bad day.