People with their cookie cutter build?

I seen so many ADC that won't bother to build any armor or health penetration even after all the cool new items that greatly benefit ADC and fighter. Am I the only Tryndamere that actually build according to my opponent build. You go armor or health, I will bring in my mortal reminder and LDR. I had a Yasuo on my team, got pretty good score but refuses to build anything but his cookie cutter build (berserker, pd, ie, shiv, bt, and reaver) and kept dying to the enemy tank. I kept killing towers and we won cause I reach the Nexus. Had I not done what I did, we would have lost despite his KDR. There a reason why your final performance grade at the end of the match is not base on your KDR.

Not that it matter anyway, people love their cookie cutter build.

Just answer one question for me. How can people be level 30 for a while or years and still be this bad?