Because trail is the only thing that affects handling?
Think about it. I do a barspin with a short stem and a long stem. The longer stem has a larger circumference, meaning that there more circular distance traveled per change in degrees. A smaller stem would lead to a larger relative change in angular position per distance rotated (twitchier, more responsive steering).
The differences are negligible. The width of your handlebars would have more of an effect probably.