My initial thought was the unlocking of vehicles, etc would come in the guise of some paid DLC. Which I expect alot would happily pay for. Then I had to think why have you chosen to leave it out. Then I see an interview with a Dev prior to launch saying it was left out for design capabilities as it takes away the teamplay element.
This I find shocking and frankly misleading which I think for alot of people has caused a reaction of how can this be case? Why would you leave them out for teamplay reasons it does not make sense.
Not satisfied with this as the reasoning, and through my own experiences testing previously led me to believe this was a tech or a capability issue. This is the only reason I can see for not allowing vehicles in public playlists. As you say you guys are not stupid you knew this wouldnt go down well and have probably tried everything to ensure the vehicles could be in but ran out of time to sort prior to launch, I can see no other reason to not include vehicles I expect it causes stability and performance issues.