Because the few people who would have their cars crushed vote. They are not a large group, but small groups voting as a block are enough to change an election. If a politician wants to keep her job she will be careful angering groups like this.

Also, in the US the 8th amendment prohibits excessive fines. It is likely that courts will look on crushing a nearly new car as an excessive fine.

Seems a bit like the ol' "cut off someone's hand for stealing" punishment, doesn't it? IMHO the punishment should fit the crime, in this case a fine commensurate with the estimated carbon impact of the illegal modification.

Societies that have draconian punishment for minor infractions tend to take the view that their punishment is fitting and proportional because it's much harder to steal stuff without hands.

Where is gets interesting is when they take a hard-line stance on some things but not on others. Like you get a slap on the wrist for theft from another commoner but if you're caught stealing fish from the lord's stream without the proper license you're strung up by your thumbs in some castle dungeon for a month.

"It would stop the practice dead in its tracks,"

Of course, because executing people when they have the tiniest amount of drugs on them has also worked so well across the world rolls eyes

Wait - I thought we were talking about crushing cars?

My point was that severe, disproportionate punishment is the law-and-order crowd's wet dream (for moral reasons) but not effective policy.