I feel that you may have left something out - what about the community?
Yes, there are new players joining all the time. This is true, and will continue to be true for quite some time.
However, anyone who plays on the server for a few days will soon discover that there are quite a large number of people who aren't exactly respectful. While this isn't only on MCSG, the fact that it's worsened so rapidly over the past year is something that sets it apart from other gaming communities.
I realize that there are games with an abundance of players with people who are worse than on MCG. For example, the COD community is infamous for their "12ies", ragers, "squeakers", etc., but that's a game that is intended for mature audiences, and by playing that game they agree that they will be exposed to things like that.
However, Minecraft - and MCGamer in particular - is supposed to be a more friendly, fun-based game. A place where you can make friends, have fun, and not deal with the type of people that you might find on COD.
A lot of parents agree to buy Minecraft for their young teens and children because it's supposed to be a kid-friendly, educational game.
Having an abundance of players who are making the community seem like a place more suited for older teens is rather negative, considering a large portion of the players are quite young and easily influenced by role models and other players. If those other players are prone to raging and trash-talking, the younger kids are either going to be scared off, or they'll be influenced by it and start doing it themselves.
The game isn't dying. The people are.
(I feel like I've left something big out by accident, I'll edit or re-quote later if I remember.)