It’s not “here to stay” it’s a feature that is used or not used depending on the level of realness wanted. Some are fine with hand waving away encumbrance, some are not.
If you’re playing a walking simulator, it is kinda part of the immersion.
If you’re running around killing every Greek god under the Sun, but suddenly you pick up your 7th weapon that’s just chains with something at the end of it, and BOOM you can’t move anymore cuz your too heavy, then it’s getting in the way. Instead of implementing encumbrance they just, limit you to 6 weapons and tada, they could explain it as “it’s too much weight” but they won’t give you the option for it to happen as slowing you down would kill the pace and feel of the game.
Baldurs gate is a DND based CRPG and Starfield is a loadscreenwalking simulator. Of course they have encumbrance.
Fair, depends on the game. CRPG’s will tend to have it in. I mean for example WotR and Kingmaker you can get a bag of holding if you buy it or put stuff into strength on characters or etc in order to not have to worry about it much but it’s still there, and not spending the money on it or building any characters with strength means you will be limited.
And you've got KOTOR and Pillars of Eternity and others that are clearly D&D derivatives, but solve the problem handily with a "stash" whose contents are never accessible in combat.
I have never understood the fascination with inventory management. I just want to find stuff, and use that stuff later on. If I wanted something as boring as my actual job, I'd just do my actual job and get paid for it instead of buying a game.
In BG3 it is a balance mechanic. Heavy objects tend to be completely OP and are used to cheese combat. encumberance limits this and even allows building your character specifically for this playstyle.
In Bethesda games encumberance is in part there to protect players from themselves. If every object can be picked up (and that is a design principle in those games) and every object has a Value, then the optimal strategy is always to grab every single object you can find and then sell everything at once. If that does not sound like fun to you that is because it is not, but still i know multiple people who play those games this way even with encumberance in place. Players will always find a way to ruin their own fun, the only hing you can do is to put systems in place that disincentivise these behaviors.
A "stash" that is only accessible outside combat mostly preserves that balance, IMO.
Most games come up with a range of ways to get around the problem, even when they do have a strictly limited inventory with encumbrance:
Zero weight quest items
Ability to run or fast travel while encumbered (FO4 selectable perk)
A pet or NPC capable of carrying your less valuable stuff back to the vendor for sale (Torchlight had this, did Diablo? I haven't played in decades.)
Pack animals/robots
Portable vendors (Skyrim had a demon vendor you could summon once a day)
Bags of holding (or similar)
Warp chests (many chests with same contents/inventory around map)
etc. ad infinitum. The fact that most games implement a variety of ways to deal with absence of an infinite inventory is kind of a tipoff that it's more of a burden than a desirable aspect of gameplay. Most of these games are holding up a carrot (or several) to get you to pursue certain achievements just to reduce the monotony of inventory management.