Marketing and sales. Pure and simple. That's what drives paintjobs and new frames every 2-3 years.
People buy a frame based on what they see on TV or hear from the salemen at pro shops and racket sales reps.
There has been some guitar talk and I think it's a good parallel. That's why "signature" models are made and marketed. They are supposed to be close to the specs of what the particular player uses.
People want to know what string gauge/type, fret wire, tuners, trem blocks, picks, pickups, potentiometers, capacitors, cloth covered wiring, pickguard material, wood type, finish type, finish thickness, cable, effects pedals, amplifier, amplifier tubes, recifier tubes, speaker cones, etc. that someone is using....
I remember seeing this one Santana tribute band on public access TV. The guy had the Paul Reed Smith Santana Signature model, amplifier, even the big triangular Fender pick than Carlos Santana uses. Even a flashy shirt. He just came off as a poser and a mere cheap copy of the Santana sound.
People want to know what the pros use because they are fans and the people they are most interested in are making money playing tennis or have a style they want to emulate. If they are successful, perhaps they can be too.
"The secret is to find your motivation every single time - your inner motivation - so I always want to improve myself..." - EV