FF is dead since many years which is not surprising imo. Making one part after another can only end like this. 4 or 5 parts is ok but over 10? Look what happened to command&conquer or other games which have more than 3 parts (i.e. Age Of Empires, Civ, Settlers etc.). Also the rendering scenes in FF are no more something special. Many games already have better ones (i.e. Starcraft 2).
the games hardly had anything in common between them, each game brought a new vision with only similar themes (chocobos, summons, moogles etc), each time the story, characters and fighting system were vastly different, all 10 installments were major successes, in fact even titles hated by some hardcore fans like FF12 and FF13 were highly successful, FF12 sold over 5.2 million copies as of 2007 and was the fourth best-selling PlayStation 2 game of 2006 worldwide, FF13 sold more than 5.55 million copies worldwide and became the fastest selling title in the franchise's history, to put the numbers in perspective this means those two titles has sold as many copies as the whole God of War series
, going by numbers alone the series is growing not dying.
so no it's not about having over 10 parts, it's about the direction the series is heading to, it's alienating their older fans and turning into a more mainstream series, in other words Square-Enix is whoring out FF rather than maintaining what made it so popular in the first place.