Depending on where you live, if you leave a big gap someone else will just fill that space and you're back to the "short following distance" mode again. Rinse and repeat...
And then when the car in front has to tap the brakes for whatever reason, the tailgater has to slam them to avoid a collision, the person tailgating them also slams theirs, and you get a wave of braking propagating backwards, eventually creating a traffic jam.