Seriously people are that annoyed about this? As far as I can tell, this is the best post launch supported game on PS4.
Sure, PD / kaz said it 'could' feature up to 400-500 cars, but you are forgetting the key word here... COULD.
Things change, priorities change. Who knows what Sony/PD have agreed in regards to next gen.
This generation of gamers are so self entitled these days. Thinking they should get unlimited content for free.
At the end of the day, there are actual people that deliver this content, think of their welfare.
And if you think you can do better, there is nothing stopping you from starting you're own game development company and giving every self-entitled fan what they want