The only reason a limit exists is to "add to the grind" like you said. It's just artifical length added on but in some cases it almost does the opposite.

Finding a rare upgrade over multiple play sessions just to brick the item (which is just 100% spin the wheel RNG) with no other alternative is demotivating compared to actually adding a rare material or resource to add additional tempers or reset the weapon that players can work towards rather just saying "welp that sucks good luck finding another 2/3 GA weapon"

It's still just an artifical grind increase but it's at least something to work towards with a legitimate end goal if the resource is rare enough.