According to my knowledge & search there are 3 main reasons behind this (credit= T-Rex Gaming) --- 1)Creates a bad image of a company or car = car companies aren't really that keen on showing their cars mowing down pedestrians, getting damaged or used for crimes. this can be the main reason why GTA 5 doesn't use real cars in game. Many car companies don't want their cars in games where they can be damaged. That's why a lot of racing games don't have damage models. 2) Expensive license= licensing cars is expensive & if license runs out they can't legally sell the game any more without either renewing the license or removing the cars from the game. & u will not be able to play with those cars (unless they renewed the license)It will require millions upon millions to use just a single brand for licensing. 3)Legal issues= this is a matter of copyright, as well as trademark law. In order to 'Brand' cars in ur game, u would need the actual logos & associated branding for those vehicles. And that would put u squarely into the trademark portion of legal discussion. It can even land up to a million dollar lawsuit to gaming companies. Despite this all some popular car racing games like Forza horizon & grand turismo can afford the real car license & car companies also take advantage & use them for their own purpose.

hi