Whether I wash my car or not, it changes nothing - the car will get dusty and rained on over and over regardless of what I do. When I first got my car I would wash it sometimes, but it's inevitably going to rain in the next day or so and return to exactly the same state. Washing it once a year is enough to remove any grease/carbon from the roads.
Why bother? I don't think it's actually "maintenance" if it doesn't maintain the car in any meaningful way.
As usual, it varies. Some outdoor environments can cause pollen/pinetar/birdpoop to accumulate and form a layer of weather-resistant plaque which slowly degrades the paint. Some indoor storage environments are open-air, which can lead to a stubborn buildup of oil/pollution/dust with a similarly negative impact.
Of course, there's also the general idea that, if you baby something, it'll last longer. Inspecting how the car looks on a semi-regular basis might lead one to noticing any number of issues -- a soft tire, a fluid leak, a faulty tail-light, etc. It's not a bad ritual to have if you rely on the good working function of such things.
With all of this being said, I don't exactly practice what I preach... Driving bores me and I'd rather pay someone else to do the associated maintenance even though I've been thoroughly taught how to do it myself. I very much belong to the "carwashes for thee and not for me" school of thought
Fashion statement is actually a pretty good explanation, thank you.