I suppose some think there is an opportunity for disingenuous posting if there is monetary gain to be had. That said, I agree with you, and knowing I have posted affiliate links without trying, I think any malice attributed to it is misplaced.
With affiliate links, I sometimes make upwards of 10 dollars every few months - enough for a free book once in a while. I'll let you guess how that compares to my salary...
I think it's pretty clear from people's posting/comment history whether they're adding them in good faith or not.
