When was the last time you played a hard game? Like really fists-clenched, "Don't know if I can actually be bothered to try again"-type hard?
They're very few and far between, right?
Even as a concept difficulty in video games was born out of the arcade's need to hoover up your spare change, or in the furtive days of consoles, something like Nintendo's "Tips Hotline" reserved for when you were truly lost in the first Metroid. Nowadays the very notion of making the consumer feel anything other than a "hearty good time" is seen as risk - perhaps because it is.
Nowhere in game marketing do we see a game's difficulty floated alongside something like an age rating, leaving the consumer to occasionally pick up a title and not get their money's worth. On the other hand, sticking with a title's mechanics and surmounting some arduous challenge that's occupied your mind for a few hours/days/weeks is a rush like nothing else - and the precise reason why we put up with game difficulty in the first place.
Indeed, this generation has seen difficulty be streamlined to be far more 'palatable', but there are many titles who've built reputations on being hard as nails, you just need to know where to look...