You can't appreciate all game elements and be a true "hardcore" gamer unless you play every genre and to some extent every game. Many people would consider someone who only plays Bejeweled, Barbie's Horseback Riding, and Sims games to not be hardcore, but why not? Who's to say that those games don't qualify? And isn't the purpose of a game to beat it using an established set of rules? If you can beat Halo 4 on Legendary level, surely you can play a game like Barbie's Horseback Riding too. You can beat it to say that you can truly master any game, but yet most "hardcore" gamers would never touch games like those.Why does a hardcore gamer need to play every game in existence?
And I didn't say it mattered, but you can't deny hardcore gamers exist, which is why I pose the question.
The purpose of games in general is to be entertainment.
As for "what games" define you as a hardcore gamer, that's a completely different subject. As you said, most won't give a flying fuck if you played a game called Barbie's Horseback Riding. I'd personally say because it probably has no challenge in it at all.