theres alot to consider about game difficulty. you cant just say that over time games have become "easier". theres plenty to take into consideration. maybe you've just gotten better. maybe controllers have become more responsive, and control schemes more intuitive. this does not affect difficulty in my opinion. entities within a game interact with each other, and the amount of skill/thought required to have them interact in a desired manner in what creates difficulty. maybe outside factors make this interaction harder, but thats not the fault or doing of the game itself. if you ask me, games have become more complex, but they seem "easier" because we constantly need more stimulation which we arent getting. the amount given to us with the NES was alot for the time, but as you play and play you gain basic understanding of how things work. as games evolve, we enhance our minds and motor skills, and with each iteration creates a building block which we refer to even now, 20-30 years later.
i wouldn't say games have become easier, i would say we've built a tolerance to the drug, and we need more.