I don't really see how vehicles are detrimental to teamwork. Whether there are vehicles or not, there will always be people who try and lone wolf it and people who try and work as a team. If they wanted to encourage teamwork with vehicles then they could implement a system where if a person in a vehicle gets a kill then other players in the vehicle also get rewarded too. Also if they wanted, when searching for a map, there could be a search option to exclude results with/without vehicles.
I'm really disappointed by the lack of vehicles, that's just a staple of the Far Cry series. At least let us use them in user created maps...