See, the thing is that I agree with almost all of this - the only thing I disagree with is wanting/expecting developers to add it themselves. Games are made to be fun, and I fully believe that people should play ANY game in whatever way makes it the most fun for them, with the only exception being of course that cheating in a multiplayer game is just a shitty thing to do. However, I ALSO believe that a developer is fully within their rights to design their game to be experienced however THEY want it to be, and it should not ever be expected of them to add in functions and cheats that break that intended experience.
If someone wants to play outside of the developer's rules, that's absolutely fine, and I even encourage it! But they have to put the work in, not get mad at the developer for not adding an easy mode or a skip cheat. It goes back to the psychology of it that I mentioned - using a cheat program or downloading a save is FULLY outside of the game itself, it's a detached experience that was clearly not intended. Having the game give you a blatant option to skip all the effort, though? That completely changes the player experience, even if they don't use it. If you've played some of the Mario games that give you the option to skip a level after dying a few times, how annoyed did you feel that it even gave you the option to do that? It's not the exact same as that, but the psychological effect is similar. Even if you unlock everything yourself, it feels like less of an accomplishment because there's a big ol' button that would've just done it for you, and if any of it was hard or annoying to unlock, you probably would have the thought "why am I bothering with this when I could just instantly unlock all of it" at some point during the experience. It's also highly likely to impact your opinion of the game negatively, as I mentioned earlier, since it doesn't exactly give the impression of "this is a high quality game, not just a porn gallery" if there's a button that instantly turns it into a porn gallery by letting you skip the game part, lol.