It may have started as simply being too lazy to pick out clothes from the closet, but at this point it's a full-blown subculture, with signals and counter-signals. Notice that if you walk the streets of San Francisco you can spot the tech workers incredibly easily. They're not just dressed down, they're dressed down in an very specific way. Toe shoes is one such way - they've achieved a cult status in our subculture and almost nowhere else.