Why do they design it this way and allow it.
Mostly because it's hard to do sound related detection with the games systems.
It's not fun playing a thief when you can just take stuff.
Meanwhile, stealing is entirely pointless because gold is not a rare resource so who cares if someone steals something instead of spending some of their 50,000 unusued gold coins that's doing nothing but weighing them down...
They're locked into certain systems due to it being based on D&D rulings. So that's why we have no stealth checks for performing actions while stealthed as they're normally done when being observed/listened to.
With the net result being a non-issue because stealing isn't broken because currency is irrelevant in the game due to how easy it is to come by. Like, CAN I steal that item? Sure, but why bother when I can just buy it and still have more than enough gold to buy every single item in the entire game?
The only actual impactful thing from stealth is combat cheesing... But it's not as if it's even necessary given how trivial combat is anyway, especially with strong builds and various other kinds of cheese.
Why bother putting lots of resources into trying to fudge around a system that they don't have complete control of (Again, because it is based on D&D's existing ruleset as opposed to their own IP like Divinity) when they could just have the retort of "If you don't like it... Don't do it". You don't HAVE to steal things if you don't want to. You don't HAVE to purposely exploit stealth in combat if you don't want to. Just like you don't HAVE to min-max characters so you clear entire encounters in the first round. You don't HAVE to exploit the heck out of Sanctuary.
I mean, personally, as someone who normally plays Rogues and likes to steal stuff in video games... I simply don't even bother with stealth mechanics in BG3 because of how unnecessary it is. Stealing/pickpocketing is pointless as I just buy anything I want (My issue is often that there simply isn't enough for me to buy for me to even be able to empty my bags of loot I've gathered, let alone actually spending the tons of gold I've got...), stealth in combat is not necessary to breeze through the game (It's simply easier to just blow things up rather than faff around with Fog/Darkness/Invisbility shenans. Maybe if I wanted to do a Solo run sure, but what's the point of doing a challenge run like that only to cheese everything with Stealth/Sanctuary anyway...)
