With two exceptions... why so few vehicle mounted champions?
The obvious exceptions being 
Though every other mounted champion is riding some type of leaving creature.
he rides himself :D
5 Comments
I think it's because it's difficult to make a vehicle mounted champion as a unique figure.
E.g. if humans build a tank that can compete with champions in league (already this is way out of whack since someone like Garen can compete... but I digress) then arguably any standard human could drive that tank. How do you develop character? How do you allow someone to connect with an individual when they could literally be anyone?
On the contrary, a champion has an identity. People connect with the champions they play (at least some).
Rumble or Corki have a unique story as to why they have a vehicle. Any other "technology" would make you wonder why Viktor doesn't just create it for himself and get even stronger. Or any other champion with the resources to buy / steal it for that matter.
You furgot one 
Close enough, I'll count that as a vehicle, but not Camille.
It probably just looks weird from an animation standpoint
If there was a guy riding a motorcycle itd look pretty strange moving at 400 ms same with most wheeled vehicles (hell corki plane looked strange at 1st before i got acustomed to it)
I want a new champion from Piltover, riding exactly that vehicle: http://universe-meeps.leagueoflegends.com/v1/assets/images/highlights/piltover-hextech.jpg
It could be so great ;A;
The lack of technology. From what I can gather, vehicles are few in number, and often user specific.