Also, another bit of speculation....
If I was Wilson and had k factor pj of pro staff rackets i would definitely have Jim Courier and Pete Sampras playing with them to enforce the marketability of my new product.
But they still play with the nCodes. Maybe because the k Factors are truly different and Jim and Pete don't like them.
or maybe because it has Roger's name on the k90 and they are too vain being former #1s.