Because most people don't go out of their way to CHEAT on unlocking their achievements?
Just a guess.
Point went over your head.
It just wasn't a very good one.
It doesn't matter that "you can". Most people don't. Most people aren't even aware this is a possibility.
I've heard the random dude like you coming out of the woods from time to time telling everyone you can cheat Steam achievements for YEARS at this point and guess what? I cared so little that I still don't know exactly how it works, because I didn't bother going looking for it.
Once again, it went right over your head. I was mentioning that even an ancient program can be used to cheat, but you can also use trainers like those readily available in popular app WeMod, or just use mods with achievements turned on and heavily cheat a thousand and one ways, including achievement toggles or things that activate achievements automatically. This was a huge discussion in other games, like Owlcat's Wrath of the Righteous, to the point where modders decided to respect the wishes of devs and not include achievement reenable in their mods, one in particular that was mostly used for QoL features, only for someone else to tell them to go f themselves and add achievement reenable themselves, and there was a lot of discussion about how the mod made the prime challenge achievement of the game (I forgot what it was, hardcore mod, solo run, highest difficulty I think) a worthless accomplishment in the community. Mods and trainers are used by tons of people in PC gaming and they're both easy ways to cheese achievements and very often are by a TON of people.
Just because you're personally unaware of something doesn't suddenly mean it's irrelevant, it just means you're ignorant.
On top of that achievements are inherently "worthless" and they mean something exclusively to the extent someone pays attention to them.
Incidentally I'm on all three ecosystems (Steam, PS4, a largely unutilised Game pass) and guess what? Steam achievements are the only ones that I occasionally check (both mine for the sake of completionism and my friends' ones just to compare what they played) and so that have some arbitrary, fictional "value" to me.
Yes, that's exactly my point. They are inherently worthless so I don't understand why people care about them. However, many people see them as badges of accomplishment, hence once again my pointing about the very different view of achievements for playstation owners. For that to be valid, their degree of challenge needs to be reasonably safeguarded. It's not on Steam. You could compare your friends' achievements, but you have no way of knowing whether they actually earned them or not. Maybe you care, maybe you don't, but you objectively can't be sure their achievements were earned as intended, you just have to assume so.
But anyway, I already pointed out that personal,1 on 1 value is actually a good use for achievements if you're just using them as self-challenge ticks. Did you even bother to read my post or were you too busy channeling your Inner Karen?