It really feels like the deal with MOBAs is simple...there is a huge generation gap when it comes to it's popularity. I know plenty of people that love them and they are all under the age of 30. Most under 25. A majority don't have a full time job, are still in a school of some sort, and are either single or at least unmarried. I am only exposed to this demographic because I have 3 step-children in that demographic. Most of my own personal friends and gaming buddies are over 30, have full time jobs, are married and have kids. I can't think of a one that plays a MOBA on a regular basis, and I can only name one that even likes the genre.
Sure, it's only my own experience and it's filled with generalizations but when I watch a stream, read a forum thread, etc...the overwhelming vast majority of the players seem to fit those criteria unless they are part of the press. This site seems to attract an older crowd, or at least it has seemed that way to me, so it doesn't really shock me that MOBAs don't really grab us by the balls or generate much in the way of positive interest here.
As someone else pointed out though, that doesn't mean the genre is on the decline or burned out. The sales and player stats seem to indicate just the opposite currently. As I have to remind myself continually, us "old folks" just aren't the target audience for whatever is hip in the gaming industry. MOBAs or otherwise.