I think it's important to have protags as their own characters in more story-driven stories. If it's a straight-up eroge, it's less important to have an actual character there; it's more practical to have a blank slate so the reader can imagine it's them having sex with a bunch of girls.
Personally, I prefer having a real character as the protagonist, even in eroge. I just think it's more interesting; I also like my protagonists to be voiced, etc. Pic related was good for this, if you don't mind BL, but it was also a pretty story-driven eroge.