Why are so many uniques part locked?

So many uniques in the game offer close to no variation between two version on the same gun :
-All jakobs pistols are grip locked
-blue uniques are all parts locked
i could enumerate plenty more but those are the first that come to my mind, is there actually a reason for this or is it unintended ?
It’s quite boring to see 10 maggies that only differs because one has a different hammer