maybe because all time periods for that are already taken except the 1999 one.

i mean, starting from after his first death in 1476 there's cva1 in 1576, then cv1 in 1691, rondo in 1792, stoker's in 1897 and the final resurrection in 1999 which is the only full resurrection that doesn't have a game yet.
and iga wants to make it all epic and stuff, so he needs time to come up with all the details. i mean, we don't want another crappy half assed game that had a good concept but failed because of poor storytelling, lack of good ideas/creativity etc right?
coming up with good ideas and stuff takes time, and when you have less than a year and lots of pressure and deadlines you'll have to make cuts or just give up on many ideas altogether because you ran out of time to flesh them out more.