Why did employer-sponsored health insurance become the norm in the US in the 1940s and 1950s?

Before WWII, only around 10% of Americans had health insurance. By the 1950s, employer-sponsored plans had become a major way Americans got coverage.

Wartime wage controls seem to have played a role, since employers could use benefits to compete for workers when wages were restricted. A 1954 tax change later made employer-provided coverage even more attractive.

But why did this particular system take hold so strongly in the US? Was WWII the main turning point, or were there other forces that made health insurance increasingly tied to employment?