> Car tires should be far more common than MC tires, atleast.

Remember, though, it was a purported list of what people buy with their tax refunds. A lot of people treat their tax refund as a windfall to spend on something fun rather than on something necessary.

I'd expect that for most people, if their car needs new tires they fall under the "necessary" category and they get them soon after realizing they need them. A motorcycle is often for recreational use, and new tires might fall into the "for fun" category, to be put off until some extra money is available.