From the WGs I've seen in the Soho walk-ups, those who refuse CG or are too eager to change positions tend to correlate with poor service overall. I saw 2 girls over a weekend in which the first one refused CG, went through the motions with no effort, and left before time was up. Next day, I saw a younger EE girl (early/mid 20s) who really enjoyed CG and we spent most of the time doing it.
It all comes down to laziness and poor service overall. If a WG refuses CG, I don't see her again.