The club's website and forums are setup for the club and it's well being. By restricting buying and selling to those who actively use the site, the club becomes more of a community, rather than just another Craigslist or ebay.
If you only need to buy and sell, then there are plenty of other websites you may use that may be better suited for your needs. If you want to be part of a club, then please stick around and participate.
