Unfortunately, we can't help you with that one. =(
All of the surveys are hosted and processed through TrialPay and I imagine some are looking for a very specific demo such as people under 150 lbs or women over 35. You could try to contact TrialPay Support to find out why you do not qualify for a certain survey, however, it's likely they don't give out that information to prevent false responses from corrupting their sample data.
Best advice I can give is to keep trying once every week or so. Eventually they are bound to have a survey that you will qualify for.