Political Views don't matter...
Yes, Orange County (OC) is the land of some of the most conservative politicians, thinkers and voters in the US. Think John Birch and Richard M. Nixon. Southern California is much more conservative than the North. come to think of it, just about anywhere is more conservative than Northern California, although it is also purple: if you took out the Bay Area, it would be like anywhere else politically, pretty much.
If the US public is roughly 49% demo and 51% Repub, the military as a whole is about 45-55. Not that different. Most people don't join the military for ideological reasons alone. So if you have a wealthy, conservative community like OC, there are probably going to be way fewer miltary per capita than a poorer, yet much more left-leaning area like East LA or maybe Brooklyn.
People from wealthy backgrounds are in the military. I'm an example. I grew up in Marin County, which in terms of PCI makes OC look like Watts. But of the 300 people I graduated high school with, I was one of two that went into the military within a year. But I was an exception, especially in the Marine Infantry. I met very few enlisted marines or soldiers with a background similar to mine. Mostly farmers, inner city people, folks from military families, and plenty of immigrants.
Right or left, if you are middle class or better int his country, the military is something "other people" do. I wonder if we'd be in a war if the military was more representative demographically?