The answer is in the rules that you have read and agreed to when you signed up:
The following forums require 10 days of membership and 15 relevant and valuable posts in select community forums in order to start a thread:
—Shared Hosting Offers
—Reseller Hosting Offers
—VPS Hosting Offers
—Dedicated Hosting Offers
—Cloud Hosting Offers
—Colocation Hosting Offers
—Other Hosting Offers
You must agree to these terms and rules before using the site.
hostingdiscussion.com
It is also in the description of every advertising forum:
10 days of membership and 15 relevant and valuable posts are required in select community forums in order to start a thread in this forum. Non-value posts, added with the sole purpose of increasing your post count, will be deleted and infraction issued.