Why do car manufacturers offer deal incentives?

1. Dealer incentive is defined as the factory-to-dealer cost which is being reduced to buy the vehicle from the company. 

2. The reason they offer these is to help a slow selling model or brand of vehicle basically saying they do this to try to boost the hype for the vehicle and hopefully the incentives will make the model sell faster.

3. The main motive behind dealer incentives is to give the dealers a low price for stocking the companies products. 

4. The main reason car manufacturers offer incentives is to help boost sales of slow-moving models. 
In order to disguise the fact the car isn't selling well, some manufactures prefer giving incentives via "hidden" avenues, such as dealer incentives and low APR financing. Sometimes car incentives are provided merely as a competitive tool and not necessarily to help sell slow-moving models. 
A final reason car incentives are used is to clear out year-end vehicles to make room for next year's models. 

To make the care and deal look more appealing, these incentives can also make you want to get other cars from there, as well as tell friends and family, or even complete strangers, about how much you love that dealership and manufacturer.