This was taught by a family member police officer that did accident reconstruction, and it was reinforced when I was taking drivers ed in high school. The general population doesn’t know and doesn’t get tested on following distance, at least not when I was tested. But here (big big capital city) 2 is typical, and anything over 4 makes people cut your off a lot. Our rush hour starts around 2 and ends around 8, the population vs the road infrastructure is just way too much, has been for like 20 years.

I was responding to a collision that happened in front of me, as a first responder (cpr + first aid certified, at the time). A Rav4 slammed into an older (90s) Corolla at highway+ speeds (traffic was moving about 70-75 mph immediately before). The corolla braked for traffic, and the rav4 did not. I’m directing people to call 911, trying to get the driver out of the corolla (it was a hard hit, the backseat was partially crushed, the trunk was non-existent, driver door jammed because frame buckling), the driver of the rav4 wasn’t wearing a seatbelt and slammed into the windshield, so blood all over it, the car, his head. While I’m trying to offer medical aid, people are slowly down to look - this was about 11 at night, still fairly busy highway - and again someone not watching, braked, swerved, tried to split between two cars in the center-most lanes (high occupancy vehicle lane, and ‘high speed’ lane). The sound of metal from all 3 was so loud, and I got to watch it, less than 30 feet from me. None of the cars involved in that collision stopped. But the car that tried to split must have been going at a difference of ~30mph above the cars slowing down. About 45 seconds later, police arrived, limited the lanes and slowed traffic properly (I only had my warning triangle with me, vs 3 lanes were effectively blocked with cars and debris. But during the busy times, you can see multiple crashes one right after the other because traffic density just multiplies the risk.

Just a mix of inattentiveness + speed/not enough time to react has been several crashes I was witness/first responder to.