The ones in my area disappeared, and they came back this weekend and I snagged another 11. I am traveling this Saturday and looked at my destination, and there is a massive dividing line between "lots available" and "absolutely nothing" with a major interstate as the boundary. I know the area and almost every station along either side of the boundary (it's where I lived for over 20 years) , and no sane shopper would have not crossed the interstate for one or two easy ones.
So my guess is that they are only accepting a certain volume of shops for each reviewer each week or two. The title implies that they have multiple months to knock all this out.
These have been one of my favorite shops so far in my ten weeks of doing MS. Make $70-80 in an evening driving a little and listening to podcasts or sports, working 8 minutes, and moving on to the next one. I just wish that the "time finished" question was at the very end of the survey.