Probably because the RNC as of late generally doesn't like conservatives doing that kind of stuff. Convention booths are great at state conventions but at the national ones they're just like everything else that goes on during the convention: staged.
They used to have lots of booths and vendors and button traders many many years ago. In Philadelphia 4 years ago the booths were all in a separate downtown convention center several miles away from the convention site. They were also horrendously overpriced and bought up mostly by donor corporations that sponsored the convention. That, and the RNC's recent tendency to pick smelly urban northeastern democrat crapholes for its conventions as of late, are the two main reasons why I probably won't attend this year.