Why is there a condition of joining referral program before getting access to the data entry / form filling jobs?

We are the only service to provide data entry jobs without any joining fees while other websites charge huge amounts towards registration fee. Additionally, we funnel all income from the data processing on to our members, making our own earnings through external sponsors.
In order to to build a confidence and relation with our members to avoid discrepancies, we want members who are serious enough to follow the guidelines and take care of the secured data not getting mishandled. 
To ensure us of your seriousness, we want you to participate actively in the referral program and receive at least one payment from us before taking part in data entry / form filling jobs. Our referral program itself is advantageous enough to not have to look for any other work.