I don't think switch to Google's engine is the cause, it's rather another symptom of the same thing — after Jon von Tetzchner has left Opera Software has changed their priorities.

Change of engine, downsizing (and old-time developers fleeing the company), and now the lawsuit to me indicate that Opera Software now favors profits over preserving company's culture, image and web standards influence.

Hippies have left, suits have taken over.