The recommendation changed from car lengths to seconds decades ago, but wasn’t well communicated fwict. I learned car lengths from my dad and then seconds when I got my motorcycle endorsement.
If everyone were leaving 2 seconds of space, it also reduces stop and go traffic that is caused, or at least exacerbated, by the traffic wave phenomenon. But that’s even less well socialized.
Not sure about your situation specifically, but restaurants requiring a credit card during reservation is on the rise to combat reservation scalping and the no-shows that res scalping causes.