Okay then: Because it's about choice and consequence.
You decide what you want to loot, if you can't fit it in your inventory then you've done your choice.
If you decide that you want... It... All.. then the consequence of your choice is that you need to do multiple trips or walk over encumbered back to the shop.
There is no tradeoff. If something doesn't fit in my inventory, I'll just come back. But there is no challenge there, it's just time consuming and game cannot expect that player won't bother doing something repetitive. Fighting is challenging, so is solving puzzles and getting out of troubble. Travelling without any obstacles is not exciting or challening, just boring. So having very high cw just skips the boring part.
Having no weight limit would mean that we could bring with us whatever we wanted.
I see the problem here when it comes to ammo and weapons, but not when it comes to loot and crafting materials.
We wouldn't need to bother looking at what we need for schematics or recepies(?) we'd just loot everything and sooner or later be able to craft what we want to craft.
What's the difference between having the items already with you than checking what you need and fetching them from your safe house? You spare some time, nothing else.
Just like there are limits in every game.
Limit to health, limit to ammo, limit to mana, limit to grenades etc etc etc.
But in new vegas we can carry 10000 ammo with normal carry weight. There's no magazine pouches that limit our ammo capacity to 6x30 5.56mm for example. I'd love to have inventory
space in addition to weight. Now everything is carried in the same mass regardless of their volume, only weight matters.
"But what if I loot stuff and put it in my house, what's the difference?" The difference is instant availability.
IMO caps and chems should have weight as well so we'd limit the amount we have with us.
Instant availability huh? If I run out of something, I stop what I was doing and go fetch more. If caps and chems had weight and it happened that I ran out of them, I'd simply go fetch more. The game cannot be balanced with the expectation that player doesn't bother doing something because it's so boring.