They're a corporation, the fan-base is huge, and apparently releasing new Final Fantasy games over and over again is a process that "works". I'm not sure why we're surprised about this announcement though: Rapture pretty much looked like a Final Fantasy from the start, we expected an announcement related to Rapture, and Final Fantasy is one of their most profitable series.
Honestly, this isn't too terrible: did anyone want Rapture to be the next Chrono game? And did anyone really think that the next Final Fantasy wouldn't be announced? Sure XIV is a bit much, but didn't we see this coming?