But I always hear that... and it just seems like an easy out. Wood movement is natural, but loose dovetails mean the initial fit was off. If you cut them right, they lock together through the seasons. My shop is bone dry in winter and everything stays put. Blaming the weather ignores the real issue with how the joints are made. Maybe the problem is rushing the fitting process instead.
Wait, what about big humidity swings in summer though? Even perfect joints can get stressed if the wood swells a lot. Do you really see zero seasonal change in your finished pieces?