Why is Deavan George not able to play the way he did when he was an L.A. Laker?

i dont understand what happened to him as he entered the mavericks team because we knew there was a time when he took over Lakers' offense(25ppg) due to Kobe's absence for quite a few games with an injury. now in dallas,critics are almost cursing him because of poor performances. i mean,i thought his aquisition is a very big plus for dallas but up to now,he's almost nothing.