The garage requirement does make sense. I would think that a classic left outside would be a more attractive target for theft than a newer vehicle. It might also have something to do with your zip code. I think paid claims are tracked by location. That's why a lot of times insurance is cheaper if you live in the country, even though you may have a longer commute to work.
It's all a numbers game on how they calculate risk. There could be merit in checking out some of the other carriers as a few others have suggested.
Good luck
John
