Because people are busy. Jobs to do, families to feed.
Because it takes effort.
Because people don't want to be embarassed. They feel the need to master the TGM lingo mastered before they can make a post.
Because some people feel they can learn just as well by lurking around and watching the free vids.
Because you need to reach a certain level of interest before you have the motivation to take the time and effort to post.
Because even though those "10 who post regularly" try to be as friendly, enthusiastic and welcoming as possible, their domination makes it somewhat uneasy for newbies to post.