I personally use Wilson Staff - but that is a throw back to when I was younger and initially won a sponsorship through Wilson (and I have stayed loyal as a result!).
But virtual clubs are just that - if the attributes are good I do not care if they are called Nike, Wilson or Bollox Brands.
As Apex said, many companies do not want their equipment for use on WGT or do not grant permission to use their brand for various reasons.
At the end of the day they are virtual clubs, and have no correlation to the real thing.