Well F1 isn't the only race BMW participate in. And in F1 BMW's role is engine supplier, Williams deserves as much blame as BMW does.
As far as I know, BMW Motorsport dominates just about every other race they participate in. They have won the Nurburgring 24hr race one-two 2 years in a row. They have also been dominating ETCC (now WTCC). Not to mention PTG and Turner's success in America.