Nokian does make a winter tire for the i3 (the R2), so it's not a total monopoly. At less than 50K cars/year, and the fact most people don't put huge amounts of miles on the thing, and it's only been around since late 2013, while yes, some have had to replace tires, there is no huge market for them, yet. When there's a market, there will be people to fill it.