There may be many reasons behind it. But, this does not mean you are not capable of it or any other thing. It certainly means that one of the following things must have happened and even if it happens, never feel let down. Just forget about it and try applying for more surveys to get better chances of taking them up.
The first and most common thing that must have been the reason for your disqualification is that every survey has a fixed number of slots for survey and when this is reached, they disqualify the rest. You may be one among them, so never delay and always apply and take surveys as and when they are posted.
The panel may disqualify people who post irrelevant things and their answers do not match the survey requirements. Always, go through the questions properly and then answer them.
The same survey may be updated more than once or in more than one forum and if you try to take them twice, then you will be restricted as users can only take one survey once. Taking it more than once leads to your disqualification.