We have all seen and heard a bunch of information regarding OW and it’s development, but I have never seen this one repeated in over the 8 years since I found out about it.
Since I found this out over 8 years ago it might be a bit off, but as you know, OW was born from the failed project Titan at Blizzard. Papa Jeff and one of the lead designers had beef on that project or something, and the designer didn’t want to implement flying cars because they thought it was tacky and wouldn’t do well.
So, when OW was developed, Jeff gave the directive to make all the cars in the game flying, as a middle finger to that developer, that’s why you won’t find a single car that doesn’t fly in the game.