It's a tradeoff, back in the era when NintendoHard was a standard, games could be beaten in under a half hour, quite regularly (watch a few no-glitch speed runs of a lot of 8-bit or even a lot of 16-bit games). They pad the game out by making it stupid hard (Ghosts 'n Goblins series, NES Ninja Turtles, etc.) or just simple inscrutably impossible (Milon's Secret Castle).

So a lot of games, even through the PS/PS2 era just were left unbeaten by a lot of players.

As games get more cinematic, development teams obviously want players to see the full game...so they make the default difficulties pretty easy, or even include a Casual difficulty for people who are more into experiencing the story than being challenged.

With certain indie titles or games like Dark Souls getting a lot of word of mouth for being throwbacks to the NintendoHard Era, there is a return of that to a degree, but a lot of developers want their project to be enjoyed, not thrown aside in frustration after a few hours.

Bioware made the stats on the Mass Effect series public a few times, and the results are pretty discouraging (at least from my standpoint). A number of people never even finished the games, and a lot of them never bothered to customize Shepard in the first place. Now imagine that with a game like DMC3 or Bayonetta (the latter of which thankfully has flawless controls, but isn't easy for the casual player).