When I think of hard games form the past I think of Castlevania and Mega Man. Just as examples, I've yet to finish either, and I put about an hour or so into them every now and again, but never dedicate an afternoon to one. I get a bit further every time, and I enjoy the pain, until I don't, then I move on. Probably to Stardew Valley...
In terms of complexity, there isn't much here, just a couple buttons, run jump shoot. It seems it's more about muscle memory and twitch maneuvers, with evolving scenarios that test your ability and train you to break/manipulate the rules in order to progress.
Games I find easier are a more Laissez Faire affair, a'la Mario Odyssey. Games that don't pressure you to get better.
It's a strange juxtaposition but the simplest games to me are the most difficult, while modern games are difficult by virtue of quantity. By quantity I mean games with complex systems, strategies, and other mechanics.
Things like Souls are "hard" because, if you were to strip away the RPG fluff, it is ultimately down to your ability, while Meatboy makes no apologies.
I think new games aren't easier there are just more easy games, fewer hard games, and the games that are inherently hard (not made harder by balance adjustment) are not as popular to the average gamer.