Manmademan
Member
A lot of the truly "Nintendo hard" games were that way because of bugs, shitty controls, and bad design. Most of the better games from that era- the Mario games, Zelda games, etc- weren't that hard relative to their modern counterparts.
There's another angle to the "games were short so difficulty was upped to inflate playtime" answer- as games got longer in later eras, the ability to save your progress became more of a requirement, which naturally took away one of the major causes of the difficulty of older games- that if you failed too much, you'd eventually burn through all of your lives and continues and be forced to start over from the beginning. A save system places a limit on how far back a game can send you when you fail, so when you're stuck on one part you can spend more time working on that part and less time getting back to that part.
Citation clearly needed here. There were plenty of games with good design that were just hard as fuck because that's the way the game was. Not "bad design", just hard.
Even SMB (yes, the first one) is pretty tough to get through without using warp zones. Zelda II isn't exactly easy either.
What about Solomon's Key? Abadox? Bayou Billy? Double Dragon III? Mega Man? Ghosts N Goblins? no one in their right mind thinks these were badly designed.
Edit: the hardest NES game I ever FINISHED was probably Milon's Secret Castle- someone just gave me that one as a naked cartridge and i had no idea what the hell was going on. The game design is just bizarre.