GigaSlime There was also a brief period where they just started calling it Castlevania to match the US releases, before they went back to Akumajou Dracula starting with Dawn of Sorrow. Dawn of Sorrow also adopted a kind of shonen anime style for its character designs and cinematics, so I’m guessing this was part of a renewed effort to court more Japanese fans?
The art style change was primarily about attracting younger fans, seeing as the series skewed order but the target platforms for the 2D games at that point were skewing younger. (That and they couldn’t afford/schedule Kojima for most of them.)
IIRC, the unification of Castlevania as a title came about because IGA felt “Akumajou Dracula” was limiting in the sense that it presupposed every game had to feature the castle and Dracula, whereas “Castlevania” is some nonsense that can mean anything and nothing, especially if the audience is a language removed, and I believe they changed back again because it’s a clunky word for Japanese people to pronounce and it didn’t really affect the sales or response to the games either way.