I think I filled a shopper quota for them, as well. They even state on their terms and conditions that they limit assignments by week, month, and year. First, the FF shops disappeared, and then soon after, all the other shops started disappearing as well, as I was doing MS'ing Full Time at one point and worked a very aggressive schedule.
However, eventually, they barred me from all shops and I am still barred from this day. As usual, they will not disclose why as they say it is confidential and that I know "some of the most confidential information within their business" .... the usual stuff they tell people. They thanked me for all of my hard work, but told me they will be unable to offer assignments to me in the future.
That was several years ago, back around 2006. I tried re-applying, and of course they told me the same thing and even years later, I can not shop for them.
They were my favorite company to work for when I was doing so and I did an enormous amount of shops for them. However, when all that started going down, I was just dumbfounded as I couldn't believe they wouldn't tell me if there was an issue so I could correct it.
However, it may very well just be quota related.