In terms of gameplay mechanics, old school zoom aiming achieves the same thing as ADS. Is getting to press your nose against virtual firearms really that important in a game about shooting werevolves and vampires?
I blame this on the proliferation of Call of Duty over traditional scifi and fantasy shooter franchises. You can fucking ADS on an assault rifle in Halo now 
If you know how to aim irons, especially illumated irons, work very well in games. Plus it looks visually neat, it more clearly distinguishes between hip fire and ads, and it's more diegetically integrated, you're looking at something that exists in the game and not a cross hair.
For a horror game irons can also restrict your fov and already limited peripheral vision, increasing the tension when you need to shoot accurately but also keep track of things aroiund you.
If the game wants you to be a cool special agent "are you a bad enough dude to save the president" then shooting accurate and effectively is what bad special agent dudes do.
It's not going to make the game worse, but it is nice to have.
no!
I'm such a bad dude that I failed at being a dude and became a trans girl about it
Best choice really fuck the president.
Especially since the president at the time was Ronald Reagan.
Imagine if the game was about infiltrating the kidnappers just to kill him.
"Are you a bad enough dude to [redacted] the president?"
Yeah, agreed. I know fuck all about guns but well-implemented iron sights can be a blast, it just feels nice. Same with recoil on a more punchy weapon, or good sounds for the guns. Sure you could strip these "unnecessary" features, and keep the mechanics of how the bullets fly the same, but it is cooler with them
Some games will even give guns "recoil" that's totally fake, just to make them feel more powerful to the player. It doesn't effect the bullets but the visual conveys "stronk!"
Theres a famous example, i can't recall which game, but players complained that one gun was too weak and needed buffs. The devs said "okay, we fixed it" and players declared it the best thing ever. Behind the scenes the only thing that was changed was to give it a punchier, more satisfying sound effect.
It was Wolfenstein Enemy Territory