The drip edge on the house, some drip edge I just bought for a shed, and a few different types of unused drip edge I've had sitting around for a decade are all non-ferromagnetic. The stuff I just bought at Home Depot even says "aluminum for light weight".
The gutters have seams and weren't formed on site, but are also non-ferromagnetic. So much for the hope of quick and easy mounting.
If I had to guess - while galvanized steel wouldn't rust on its own, it's avoided due to the possibility of being in contact with other metals that would cause it to still rust. Roofing nails are galvanized, but they're supposed to be dry under the shingles.
