People with social anxiety (especially) need time to "feel" out a certain forum or situation.
It's tough to be a "joiner" and many would rather be a "lurker" than jump right in and start discussing the topics at hand for fear of being "exposed." They could be afraid of rejection, saying something "stupid", or maybe, just maybe, they want to see what this site is all about, and get a feel for the members here.
Remember, we're all here for the same reason. For some, it takes a bit of time to join anything. :wink: