In a word...$$$$$$$$$$$$$
Top pros are usually required by the terms of their endorsement contracts to state that they use the equipment (i.e. paintjob) being promoted at the moment. To say the real specs of their racquets would be to publicly admit that they are not using what they say they are using. It would also "give away" that the highly-marketed, "technological innovations" being promoted by their various labels are very much less important than the PHYSICS of static weight, swing weight, flex etc.
Please also note that paying someone to claim they are using a product that they are in fact NOT using violates Federal (and often State) false-advertising laws. However, these laws have gone unenforced for a long time in the tennis world (golf is another sport where these violations are ignored). It is interesting to note that a consumer protection group did make some headway in a lawsuit against Nike, because Nike was selling a golf ball that it claimed was being used by Tiger Woods even though he wasn't using it. The lawsuit ultimately forced Nike to admit to the practice and further lead to their selling the real ball that he actually used. I doubt that Nike considered this lawsuit anything more than a minor embarrassment and a nuisance.
Ultimately, this practice hurts the sport of tennis a great deal, and it represents just another area of our modern lives where the interests of individuals are not protected by the very laws and law-enforcement mechanisms that are designed for their protection. Rather, "corporations" are allowed to blatantly violate the law in order to pursue the highest possible profit.
One of my personal heros in Mark Phillipousis. After a dispute with Head, Inc., he began spraypainting all of his racquet frames black, rather than give them free advertising. For a while, he also went without any kind of a clothing contract, and he was covering the logos on all of his clothes, bags etc.
It would benefit the sport a great deal, if the ATP would publicize the specifications of each tour players' racquet, and string tensions etc.
Fortunately, there are places like this forum. With a little research and some common sense, one can get a much more accurate idea of the racquets the pros are using and employ the knowledge towards his own game.
BTW, thanks to all of you well-informed posters who have posted the specs and tensions from the various tournaments you work at. It has helped me immeasurably.
GG