Serj Tankian is to blame for the lack of new music from System of a Down, according to the band's bassist Shavo Odadjian.  In vicious Facebook post (which has now been deleted), the bassist attacked his singer.

The post (courtesy of Loudwire) read in part:

"Its not us(meaning Daron,John Or Shavo!! Its Sej, who doesn’ want to do a new album!!!! so please stop harassing us about it!!!...Sorry folks!!! we’re trying to get a new album out, its just not passing Serj’s RULES!...Just remember, Hes been holding us back for 7 years so far.. wanna wait another $-5 years? or shall we release a record without Serj?...I dont want to make a record without him… but if he’s not down? should the 3 of us just sit and wait?? Not cool!!!!!!!! i want the fans from all over the world including Brazil to tell us what they think.  No System? or System with with a new singer whos just as good if not better?"

That was on Shavo's page.  On the official System of a Down Facebook page, the band (or probably management) responded:

"Earlier today, Shavo posted a few statements on his personal Facebook page that do not reflect the sentiments of System Of A Down as a collective band. These were misleading statements that were made during a temporary state of bad judgment on his part alone. To be clear, the full band lineup of Serj, Daron, Shavo and John will be performing all scheduled tour dates. With respect to new SOAD music, although we have not agreed on a timetable for a new album, we all believe that having the four of us do it together is the way to be true to the band and our fans."

That last System of a Down album was released in 2005.  Since that time, Tankian has released four studio albums.