Searching the California Craigslist like I do I'll say we just don't have the quantity of old European bikes like Europe does. We do have a ton of Japanese bikes though and they had aero brakes by 1987. For the US and California locale in particular it's helps because we don't have many quality, over the top cable routing equipped bikes in comparison to literally anywhere in Europe. I noticed this when doing my own prep for the race so it's just my personal conjecture as to why.