It's also just like... gaming is different now and the culture is different. Games take themselves more seriously in ways they didn't use to in say the late nineties/early aughts. There was a whimsical air to early games where you know, it wasn't a big deal if you used cheat codes, you were just having fun by yourself at your PC. These days games are to a much further extent curated experiences that take themselves seriously and where it's important to get the full "artistic vision".

Also in the pre-internet times it was often a benefit to have secret stuff like cheat codes to generate buzz. I'm reusing an example from elsewhere in this thread but it was good word of mouth at the school/work place to have people spread the word about neat things like the Big Daddy car in Age of Empires or whatever. These days you could just find it with a quick search, and the magic and appeal of that kind of stuff is gone.

And again I want to pushback on the MTX angle a bit simply because we are still far from being at a stage where every game has them, even AAA games. Hell, if anything the GAAS and MTX wave seem to be abating. I would be much more on board with your argument if microtransactions were absolutely omnipresent, but we're not there at all, even in the AAA space. And I could absolutely see a retro-themed indie single player game add some old school cheat codes, I actually think at this point it would be a pretty solid marketing trick.