The shareholders are a disparate group, with no single voice, it's like herding cats. in truth the pressure to reign in executive pay mostly comes from hedge fund managers (as you know). Shareholder power is often talked about but is rarely decisive. Boards do everything they can to avoid executive pay even being discussed at AGMs, even getting it on the agenda is a near impossibility task.
Shareholder revolts are rare not because shareholders are content but because of the obstacles they face in pulling them off