I think it was traditions, eras, and weather that dictated training somewhat. The northeast, mid-atlantic, etc.... developed it's physical culture in the shadow of York Barbell, so you get more of a weightlifting/powerlifting feel to a lot of the gyms there, just guys grinding it out, more strength and numbers based. Also the weather is ho-hum for a good portion of the year compared to California, so you get a lot of guys lifting with more anger from just being cooped up 2/3rds of the year.
Meanwhile, a lot of California bodybuilding sorta fell under the influence of Weider philosophy and California's general mellowness to my eye. It always seemed like California was like "lets lift some weights, and then go down to the beach, and chill". More of a fun feel to it.