Offensive/Defensive disparity between conferences?

[TwentyOne920]

Last season the top 5 offensive teams by ORtg were San Antonio, Oklahoma City, Denver, LA Clippers, and Chicago. Only Chicago's from the east.

The top 5 defensive teams OTOH were Boston, Chicago, Philadelphia, Miami, and New York. No west teams here.

I know schedule plays a factor in why the East is better defensively (playing teams like the Bobcats twice instead of once and playing teams like San Antonio once, given the lockout schedule) but conversely why are the Eastern teams also poor on offense?