Cars tend to require tools by default, but a lot of bike parts can be removed just with your hands. They’re also a lot lighter and smaller, so they’re easier to carry and hide. To take the wheels off a car, for instance, you need to jack the whole car off the ground - with a bike you can just hold it in place.

The ratio between profit and police attention would be terrible for the "innovator". But it happens nonetheless, just like roof tile theft, wire theft and so on.