>>28603410
Because there's a mental illness epidemic in this country. Everyone's on edge and doesn't know how to properly process their anger.
Also, American driving culture is toxic as fuck and almost every driver sees every interaction with another driver as a contest they have to "win" by being more aggressive than the other guy.
Self-importance is another. Everyone thinks they're more important than everyone else and this gives them the right to weave through traffic, not use their signal, tailgate, etc.