It’s more effective in controlling the behaviour without interfering with other aspects of the game. You can base the hard cap on whatever you want, be it strength or intelligence or whatever.
The idea is that the “Let’s make this stupidly heavy and huge so the player can carry less of it” affects things other than the item, leading to further unrealistic situations and side effects.
For example, if you add in the future an item that increases how much weight you can carry, then the item is undoing your balancing, and now you have to either, rebalance the extraweight lifter around the arrows (reducing it’s effectiveness for everyone just because of them, probably making it useless for anything but carrying the extra arrows) or further increase the weight of the arrows to compensate (Which would make it so a player without the extraweight lifter being weaker after the release of it, without guarantee of obtaining it.)
Each arrow is also reducing your capacity to carry unrelated items due to their extra bulk. Nerfing unrelated items by limiting your ability to carry them (And, if you keep going to this solution, you will also change the weight and volume of this other affected item so “you can carry more while holding the arrows!”. Which complicates everything by now making it much easier to carry in bulk by the people who are not using the extra heavy arrows).
The clean solution is to implement a cap that only affects the arrows in a vacuum, that way, their “overpoweredness” is contained without unnecessarily affecting other aspects of the game which are currently considered to be balanced.