You're making it up now.
How many types of theft are there?
How do we differentiate them, by adding an adjective, either before or after, as in 'theft in breach of trust', 'theft of metal', 'theft of art', 'theft of pets' 'theft by deception', etc.
"Theft" is the noun, and the adjective describes the type of theft, as in "Theft of cars", or "car theft".
Moreover, theft is taken to be stealing without the use of force. When the use of force is applied, it becomes a more serious offence, an aggravated offence. Theft involving the use of force becomes robbery.
So "theft of cars" or "car theft" is the lesser of two (or more) evils.
So theft of cars, is not an aggravated offence unless there are other offences committed during the driving.