Colors change year to year too.
Ultimately, it has to do with gear ratios. If your bike has the gears to go as fast as you ever ride and the gears that you need to get up the steepest hills that you ever ride on, you really have nothing to gain by changing them.
One other thing: It's the motor. If you put a Ferrari transmission into a Yugo do you think it would suddenly go 150 MPH? Changing your bike's gears probably isn't going to suddenly make you a lot faster either.
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My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.