Is this a West Coast thing or just a British Columbia thing?

I can't quite answer that, but I can guess it has something to do with the weather. In Manitoba and northern Alberta (where I spent my childhood Hallowe'ens), it's usually cold enough that you need to wear your snowsuit under your costume. I can't see it being much fun to stand around outside playing with fireworks in such weather.

Then again, on New Years' Eve in Winnipeg there are always fireworks downtown, and the temperature is often -30°C, so maybe that's not a good argument at all. Oh well, I tried.