Why wont my arms grow

Training for 2+ years now, started off with a high volume training approach but arms were at about 14 .2 inches flexed. Started high intensity low volume training + went on a 6 month long bulk to accommodate, got my arms to ~14.8 flexed. Question is what am i doing wrong? I usually do 8 sets to failure for both triceps and biceps per week, my curl is pretty decent i can do 40s pretty easily with good form, and my pushdowns are pretty good too doing 75 lbs pretty easily for 10 reps (both of these with slow eccentrics). What should i change?

Heres some pics https://imgur.com/a/wyxIxIw