I have the opposite experience with most games. I remember finding the earlier Capcom platformers and the like to the pretty difficult, or at least requiring some time commitment to complete. Nowadays I can pretty much breeze through them in a couple of hours.

The difference is mainly between games that were difficult to beat because they required a certain dexterity that's second nature to some of us now, and games that were difficult to beat because they just weren't designed in a way that your skills as a player would increase your chances of winning. I'll use Double Dragon 3 and Megaman 3 as examples here:

DD3 for the NES is one of those games that people universally agree is a hard game to beat. But it isn't hard because it requires the player to be skillful - It's "hard" because the way to win is unintuitive. Most people would go play through a sidescrolling beat em up that gives you tools like standing punches, kicks, and grapples to use those tools in tandem to defeat the hoards of mooks on the screen. In fact, the game design punishes you for doing this. Enemies will randomly recover instantly from hitstun and interrupt your attack string for massive damage. There is no way for the player to predict or counter this. If it happens enough times, the player has to restart the level. Needless to say, a whole lot of people had to replay a whole lot of levels because of this. But despite this, the game wasn't difficult.

The solution was to not use those tools. By walking forward and jump kicking every enemy in the game, you can pretty much get through unscathed in less than half an hour. As soon as you stop playing the game as it was (poorly) designed to be played, and start using your dexterity, awareness of enemy AI, and amazing superhuman spatial awareness skills ("Will the hitbox on my foot hit this mook's head at the end of my jump arc? Yes? More jumpkicks"), the game goes from unbeatably hard to something fun and easy to do while casually waiting for your Steam update to finish.

Megaman 3 was "hard" for a different reason, but still not genuinely difficult. The game boils down to rote memorization. "Remember to move in the opposite direction immediately after jumping over this chasm, because a mook is going to jump up from the pit and insta-kill you." The boss fights are the same way, as there is no variation to their attack patterns. Which, when you haven't memorized the pattern and are made to replay a level until you do, gives you the impression that the game is difficult.

Both of these games were developed in a time when game design theory was focused mainly on getting people to put more quarters into a coin-op. A modern beat-em-up style game like Bayonetta would be a fun arcade addition, but wouldn't do much in the way of making money for arcade operators, since the game gives you defensive options to reasonably keep yourself from dying if you have the dexterity to make good use of them.

The Castlevania games are also good examples, especially the Igarashi titles (SOTN and the like). They're still hard in that it takes time to get to the point where you're able to dodge and counter enemies and make effective use of your items without taking a Medusa Head to the face in the middle of your backdash. But it's insanely rewarding once you do get that good at the game.

tl;dr: If a game was designed to give skillful players an edge, you will find them less frustrating now that you've accrued all those skills over the years. But if it wasn't designed that way, it's going to be just as frustrating (Unless you game the system).

And yes I made this same post last year.