LogFAQs > #970036502

Healthcare is tied to work, because of wage and price controls at the end of WW2.
Employers couldn't pay more, so non-monetary compensation was a workaround.
https://www.nber.org/bah/2009no2/employer-sponsored-health-insurance-and-health-reform

here's the important part:

First, during World War II the War Labor Board ruled that wage and price controls did not apply to fringe benefits such as health insurance, leading many employers to institute ESI. Second, in the late 1940s the National Labor Relations Board ruled that health insurance and other employee benefit plans were subject to collective bargaining. Third, in 1954 the Internal Revenue Service decreed that health insurance premiums paid by employers were exempt from income taxation.