Another theory: people stopped leaving things in their cars, so this form of crime became less lucrative.

That's not what the numbers quoted in the article for police activity suggest. The police adjusted the risk/reward ratio toward risk for offenders. They also worked to get the most egregious offenders which also had an outsized impact.

No need for alternate theory.

Catching criminals and punishing them actually does work to reduce crime.

another: maybe fewer people are commuting to work in the city

alternate: cybertruck windows don't break