Bad at arena

Because it's so quiet here I guess I'll post something: I don't understand why I'm so bad at arena. I hit legend once in constructed a long time ago (Un'goro) so I understand the fundamentals. I've made honest attempts over the years to get good at arena. I watched a lot of YouTube videos on how arena differs from constructed, studied tier lists, etc. The best I've ever done 11 wins, but at my best I was probably averaging 3.5 wins. This weekend I played ~4 runs and had <3 wins each (but I'm returning after a long break).

I just can't quite figure out what I'm doing wrong...