Why is there a limit on the amount of Traffic Exchanges that I can submit to the Downline Builder?

The purpose is so that one person does not submit thousands of Traffic Exchanges so that it blocks everyone else from submitting.  Being able to submit a Traffic Exchange is a privilage that all upgraded members are able to take part in.  The higher your upgrade the more Traffic Exchanges you can submit.

As the Traffic Browser Team begins to approve or disapprove the suggested TE's that you provided you can start adding more TE's.   Let's say your limit is 3.  You can submit 3 Traffic Exchanges, then after admin approves 2 of them, you will have 2 additional credits to submit more.

At this time free members can only vote for suggested TE's.  Upgraded members have more rights to add more based on their membership level.