Video games get delayed all the time, whether because they need a little more time in the oven, or because publishers knows that expectations are extremely high and it cant just slap a big brand name on something and call it a day.
Final Fantasy XV is a game that Square Enix delayed a lot. The backstory of the games development is far too complex to really get into here, but it started life all the way back in 2006 as a spin-off of Final Fantasy XIII called Final Fantasy Versus XIII. Almost all of that material was eventually scrappedwith some of the bones ending up in Kingdom Hearts III and Final Fantasy XV didnt come out until a decade later.
Even then, Square spent years continuously patching and updating it after the fact to fix, add, and change certain things that were either incomplete or were received poorly on the initial launch.
Source: N4G PC Final Fantasy XV and the joy of games that arrive unfinished