Where do blazers come into the equation?

As a t-shirt and jeans, t-shirt and khakis and button down and khakis kind of guy, I've never understood the whole "vintage" look that people my age and younger have adopted in the last few years. ("Vintage" as in looking like you bought all of your clothes at second-hand thrift stores specializing in stuff from the '70s and '80s.) One of the outfits I see on men and women is a blazer/sportsjacket combination with a shirt and jeans. Yes, a blazer, a coat traditionally synonymous with an outfit consisting of slacks, shirts and ties, with a shirt (usually a t-shirt) and jeans. How in the world did this become fashionable?

I think of a coat as a layer of clothing that adds warmth to the body. Yes, that's a very big "duh!" line, but I bring this up because I see people wearing blazers year-round. This brings major puzzlement into my head, especially in the area that I live.

For the non-Texas-resident readers, Dallas usually gets bone-chillingly cold between November and March. That's only five months, so the other seven months are filled with various stages of warm conditions. "Why the extra warmth?" I ask. It's not that cold indoors, especially at shows and parties.

I've never understood fashion trends. I don't keep an eye out for what's hot and what's not. As soon as something is "in," it's "out." I've never wanted to wear tacky clothing. I've always wanted my clothes to fit (I need space and I don't like clothes that are tight). I've always wanted to wear clothes that I've wanted to wear (I will admit to wearing the trendy HyperColor and Stussy in middle school, but they were designs that wanted to wear). On top of that, I've never wanted to wear more layers than I needed to.

I see this blazer-with-thrift-store-clothes contraption on the bodies of a lot of band members. Here is a pic of Death Cab for Cutie, with frontman Ben Gibbard (second from left) is such attire. What he wears has nothing to do with the quality of music that he makes with his band (which I happen to enjoy), but I roll my eyes every time I read an article with a picture of him in that get-up.

And to think, this kind of look was once in vogue. I may be comparing tractors and motorcycles here, but tacky fashions are gonna come and go. Why I would camouflage myself in one is beyond me.