Anyone know why Rockstar doesnt just add the REAL version of their cars?

I was wondering why they don't just contact the real car manufacturers to get proper licensing. Grand Theft Auto is one of the top sellings games/if not THE top selling game of ALL TIME. Not to mention it's been running for more than 10 years and still has full lobbies. Look at these cars for example, they might as well have thrown the real badged on them: