I’m thinking it is due to the shapes used… bikes have lots of long tubes, if these were dimpled, then wouldn’t the turbulent flow caused by the first part of the tube start to cause drag on the next bit?
then there’s the question of speeds too, golf balls can fly about at up to roughly 150mph, (according to a 2 second google search!), the mass flow of air across the ball at this speed will alter the reynolds number of the situation.
Sooo, the dimples may not actually provide anything but drag at lower speeds, speeds more comparable to bike speeds.
This is, of course, just guesswork. You could verify things by giving your bike a nice think coating of hammerite, and see if that helps!!! : )