A couple more, applicable to me:
1. Uncertainty if provider wants a review. I have never been asked to leave a review, and only a couple times have I felt like I should ask to leave one. However, there are certain providers, particularly those that are somewhere above UTRs and somewhere below full-advertising indys, where I just don't know their preference, so I would rather (perhaps for reason #1 you noted), not comment.
2. Nothing remarkable to say. I will always review if I had positive experience, or a negative one (i.e. B&S, scam, etc.). However, there have been some situations where the experience may have been "blah", but I would not want to leave a negative review, as that may negatively impact her opportunities, even though it may have been an off day, or just poor chemistry between us. I am not very consistent in the application of this rule.
Also, TER gets very strict with their policies; I have had to make edits and go through re-approvals many times before to get it through their moderation. That might frustrate some folks.