Ya, what’s up with that? It is totally true, but I’ve never been able to figure out why it’s true like that, given its huge unfairness. Is it just punishing people who get laid off from their job and have to go on Cobra? Likewise, are independent contractors just SOL?
These high income taxes were politically popular, but companies still wanted to compete for workers. So they found all kinds of loopholes for extra benefits they could give employees at a lower tax rate (or at no taxes at all). Sometimes they even lobbied for those loopholes, too.
See https://en.wikipedia.org/wiki/Health_insurance_in_the_United... for a brief overview, and perhaps follow references from there.
Employers were not allowed _by law_ to pay their employees competitive wages, so they offered benefits which weren't restricted.
Even after the war, this was still a benefit to employers: the cost of benefits paid by the employers could be deducted from their taxes, but employees didn't have to pay taxes on it (unlike wages), so it was more efficient; also, changing jobs meant changing health insurance plans, which complicated job switching for employees.
(BTW, the supposed "high tax rates" were paid by almost no one, in part because they only applied to the highest tax brackets but also because of numerous tax deductions.)
Of course, both what you said and what I said still doesn't explain why benefits weren't taxed (or at least not as heavily).
Btw, I remember growing up in the 1990s in Germany that having a company car used to be a big deal as a perk. I don't hear about that as much anymore, I suspect it's because the relative tax attractiveness of benefits vs straight up cash changed over time; I remember some loopholes being tightened (if not closed).