Visiting SF a few years back (pre covid), I was surprised to see how many cars had no license plates at all. The owners weren’t particular about keeping a low

Visiting SF a few years back (pre covid), I was surprised to see how many cars had no license plates at all. The owners weren’t particular about keeping a low profile or not being noticed. As an outsider, it seemed to me perfectly legal to have no plates. Turns out, having asked around, it’s all those people going over the golden gate bridge and not wanting to pay the toll and instead rather taking the risk of being caught without plates - obviously cheaper than paying the daily toll. Is this in anyway related to cracking down on this practice?