Really, because it feels so freakin' good when you ride a bike that's made specifically to fit you.
I had my Bike Friday custom made, and whoa! Riding that bike vs. my Specialized Sirrus was like the difference between buttering your bread with butter vs. motor oil. I don't have to worry about the handlebars being too far apart, the drops to be too low, etc. It's a perfect fit.
Koffee