Why is gnar not played more?

I just got through a game as Gnar. What I find interesting is my stats and end game stats. For one, I did the most damage, and I also took the most damage. Sounds like a standard top lane carry. But my build is what is confusing. I built a Black Cleaver, Frozen Mallet, Banshee's Veil, Dead Man's Plate, Warmogs, and I was finishing Randuin's. In Mega Gnar, I had 6100 HP, makes sense, as I was stacking health. But i also had 217 AD, 1.38 AS, and 422 MS. The fact that i was so tanky but could do so much damage was rediculous. I'm just wondering why nobody plays him with end game stats like that.