Poor Sheva, she ain't ever seeing another game. That's what happens when you give a character no personality.

Pretty much. Billy's also never shown up outside of RE Zero or the chapters in Umbrella Chronicles which just told an abridged version of Zero's plot. Barry took 15+ years to show up again after the minor (and also possible to not even get) cameo in one of the original RE3's endings (Gaiden is non-canon), finally getting a playable role in Revelations 2. And before Barry, Sherry showing up again in RE6 after not being seen since RE2 (or the bits in Darkside Chronicles retelling RE2's story) was a pretty big surprise since she had effectively disappeared as a character for about 14 years.

Not to mention the characters from the Revelations games that haven't been seen again since those games like Parker, Raymond, and Natalia (Raymond and Natalia especially since the post-credits for both Rev 1 and 2 hinted that they may have greater significance in possible future plot lines). O'Brien did shockingly get a nod in RE7 so we do know Capcom hasn't forgotten them (RE7 also referenced a character from Outbreak, meaning the canon status of Outbreak has sorta had its head turned).