Both A and B.
Hidden gems are more likely the one 3rd party or even a 1st party company that released a brand new game that never get previews and eventually be seen at stores but found out the artwork looks dumb and we never dare look at the back of the box to prove the game could be good, and mostly of all, marketing and publishing issues.
Publishing Issues
Sometimes the developers who can't find a good publisher to release the game and then found one who would keep publishing games that would lead to a bad game. Companies like LJN, Acclaim, THQ, Ubisoft, Activision or Limited Run would be the prime suspects of these publishers that these amazing developers would fall into and consumers would pass on these games thinking it will be bad or not sell well at all because of those publishers.
Marketing Issues
This would be the main issue. Whenever those hidden gems come out, a big major IP release like Mario, Sonic, Zelda, Kirby or whenever Rockstar pulls out a GTA game out of nowhere, would eventually steal the spotlight. Whenever a release date, the same day, same week, same month, those hidden gems will then be locked in the closet and be forgotten. Another part in marketing issue is whether the developers like Nintendo or Sega will release any of their IPs outside of Japan and the US division tries to market it either from TV or pages from a gaming magazine or comic book issues.
And sometimes, it's very rare to catch them on tv during commercials or seeing the ad of a game from a gaming magazine that would show very disturbing and disgusting images with or with no gameplay images at the corner. So we do not know what the game is about or how the marketing team does not know what consumers want. In which, the games we got to play due to those issues, are hidden gems. We just don't know what hidden gem we actually played because there's just too many major games that were marketed so much.