It's not that he didn't work on them; for KCEK's games, it's that they were made as side-stories with no connection to the existing timeline in the first place. The N64 games are dropped in the middle of the nineteenth century with no accounting for the hundred-year rule, and Circle of the Moon pointedly features a storied family of Dracula hunters who aren't the Belmonts, who hand down to the next generation a magic whip that isn't the Vampire Killer. Legends infamously supplants Castlevania III as the Belmonts' first battle with Dracula (a bad idea in the first place, for multiple reasons) for the sake of inserting lore that retcons all subsequent Belmonts as Alucard's progeny.
On stream the other day, I was trying to keep track of how many "no, really, THIS was the first Belmont" moments the series has, and boy, Konami sure did love going back to "this is REALLY where it all started" on this series, didn't they? Even if we don't assume we're meant to think Simon is the first Belmont to kill Drac, there are still AT LEAST FOUR different versions of "this is the beginning of the Belmont story" out there, at least two of which make the world a lot smaller, which I kind of hate on its own, but also in specific ways I hate.
-There's a brief window where
Castlevania: The Adventure (1576) was chronologically the first in the series, but Dracula's Curse came out so closely after, that I don't really think Christopher is meant to be THE FIRST BELMONT, because this had to be developed contemporaneously with CV3. Still, worth mentioning.
-In
Castlevania III (1496), we're told Trevor/Ralph has power to kill vampires, but it's heavily implied he's the first to destroy Dracula, thusly cursing his own bloodline. Also heavily implied that Sypha is the matriarch of the Belmont clan.
-In
Castlevania Legends (1450), we're told that, no, that's not right, Sonia Belmont was the ODK (Original Dracula Killer), and, as Kishi mentioned, that she boned down with Alucard, so not only are all the Belmonts part vampire, but they are also SPECIFICALLY related to Dracula himself, which... why? No. Stop.
-In
Castlevania: Lament of Innocence (1094), we're told again that, no, that's not right. Leon Belmont was the first Belmont, 400 years before Trevor, and also, his best friend is Dracula, but I guess that's fine because who would remember that after hundreds of years, and it doesn't tie them by blood.
-In
Castlevania: Lords of Shadow (1047), we're told yet again that, no, that's not right, either. Gabriel Belmont was the first Belmont, and also
Trevor is his son, and also also Trevor is actually Alucard for some reason, because Gabriel Belmont IS fucking Dracula. Like... come the fuck on with this shit.