A lot of the older members were around 13-14 in 2008-2009, so a lot of them are in their final years of High School. Due to to High School being more demanding than Middle and Elementary (Lower secondary and primary for you International peeps), most don't have time to post on MPGH during the school year. Since Summer is here though, they're able to rise from the grave and get back online.
Past about 2010 and 2009 though, most earlier members are perma-dead, as they've become adults and have other interests and responsibilities.
He responsibilities. I'm gonna have kids before I even think about leaving MPGH forever.