There’s more to it than that - there’s a lot of research involved. Other factors involve:
Nobody does anything at the exact same time.
What’s a turn signal
I’m the main character!
Hold on my phone’s ringing
I’m getting in front of you if it kills you!
Shit I’m gonna be 1 minute late for work!
Fuck you in particular!
One snowflake fell, time to panic!
ALL the snowflakes fell but who cares I’ve got 4wd!
Fuck this traffic, I’m taking the shoulder!
CRASH
Oh shit a cop everybody slow down.
And more!
Chief offender is the cascade effect. Basically, there is a minimum convenient distance one can follow another at a given speed in given conditions. If thee guy in front of them does anything but keep going, they should be able to deal with it without slamming on the brakes.
But if people follow more closely than that, especially because the traffic volume increases, then when car A slams on their breaks, so do cars B, C, D, E, etc. then because everyone’s reaction speeds are marginally different, by the time you get to car F, everyone’s come to a hard stop, while car A goes on, oblivious that they created a traffic jam that may or may not have been inevitable.