Why the government program OSHA did not noticably reduce worker fatalities

This picture says a thousand words about government efficacy (immeasurable? Without that vertical line, there's no way to tell when OSHA started or when it finally started making a difference):

I got here via Marginal Revolution. In the same post, we learn:

Annual OSHA penalties for safety violations (2002): $149,000,000

Annual Workers Compensation Premiums (2001): $26,000,000,000

Estimated Annual Wage Premiums for Risky Activities (2004 dollars): $245,000,000,000

His point: Market incentives for worker safety dwarf legal incentives, which in turn dwarf regulatory incentives. The level of safety we see in the workplace today is about the same as the level we'd see if government just looked the other way.