I believe the wide flat bars on tracklocross bikes stems from wide flat bars being very popular in the entire fixed gear scene for the past 4 years or so as a counter culture to the skinny bars that were made infamous with fixed gear bikes in the early 2000s. Although I have very wide shoulders, I never liked wide bars for some reason. I have a tracklocross bike and I was running skinny drop bars all the time, but recently replaced with skinny, cut down riser bars.