Well, that is not 90% of the total income.

If you google income tax rate history you will discover that around 1990 the Marginal tax rate was 92%. No one quit working, certainly not the rich that was affected and don't think anyone was in that bracket back then.
Apparently, it topped 94% in 1944.
I had a link to an interactive table that showed around 90+% around the 1990s but cannot find it now.
Tried to find that graph but not finding it so maybe it wasn't around 1990.