Could be VW UK with the tyre contract then.
Its definitely a contract thing and almost certainly a price point.
If that contract was an exclusive one for say 18" tyres on a particular model, then they couldn't offer tyre options... and without the lockin, I expect the price would increase.
I know stuff like that goes on - my work is like that, we use some parts that aren't the best purely for a contract reason and even though our customers often later swap them out, we couldn't do that for them.
