Well, you're comparing him to pretty much the most prevalent protagonist character in the series, at this point. Ol' Rich is still plenty prolific himself, probably around the same level as Simon.
Anyhow, it's more about the context of his appearances. I know his Portrait showing and especially being made a playable bonus character in it rubbed some people the wrong way because it was seen as a quick and cheap way to add more content, Richter having the most modern sprite out of all the Belmonts, so it was no big deal to just slap him in. They went for convenience instead of doing something actually relevant to the subject matter, like a John/Eric mode or whatever.
The rest of the distaste probably stems from being featured prominently in two of the (totally justifiedly) most popular games in the series, both of which have seen their share of ports and rereleases along the years. A victim of hype, perhaps.
He's just around a lot despite only two 'real' starring roles.