It was a game aimed at the low intellect. It made money because graphics are all that matter these days and because it was called Final Fantasy. Compared to FF7-10 it was a massive dumbing down, and the reason they thought it was great removing 2 playable characters in XIII is because people like yourself salivated over XII.
I am tired of watching this series sink further into brain dead because people continually accept these mindless releases.
look I think we are going to continually disagree on the merits or lack thereof of ff12 so I will leave my personal feeling on that game aside. I will say though, you mention that "Compared to FF7-10 it [12] was a massive dumbing down" first, these four games play very differently as every final fantasy should at least to an extent. If you consider 12 to be dumbed down from the previous releases then you could say that 9 was dumbed down from the previous release. ff8 had what some woud consider to be a complex system namely junctioning, whereas 9 was much easier to pickup and understand how to play and how you learn techniques.
Every final fantasy fan or rpg fan will disagree on what is the best game in that series or genre, many people dont like final fantasy 7,8,9 or 10 (the four games you seem to believe were a pinnacle of the series) in fact it is thought that 7 was "dumbed down" compared to ff6. I like 12 even though I agre it has its faults, but I also enjoy ff7-10 and the games before them which also had faults of thier own and I am sure I will find merit in the so called "mindless releases" that will come in the future as many other people will as well
p.s. please don't imply that I have a low intellect simply because I like a videogame that you don't