Heirlooms instill a sense of personalization that is a source of pride for most players. If you feel like they are just a meaningless grind, you probably loomed a Kuyak and a Longsword. For instance, there are certain weapons that are rare enough that I am excited when I find one on the battlefield. And I can usually guess the owner due to this rarity.
I think Final Boss' texture pack has a lot to do with the fun of finding rare heirlooms on the ground; his textures for many weapons look amazing, and I'll equip them just to admire.