If you look at the bend points, you'll see that high income career earners subsidize low income earners with 75% marginal tax rate. I forget the 1st bend point marginal tax percentage, but it's around 60%.
I say marginal tax rate because people below the first bend point get 90% credit and people above the 2nd bend point only get 15% credit. That 75% credit is used to subsidize lower income individuals.
I guess, technically, it's a bit less than 75%/60% since we also subsidize our own below the 1st bend point dollars, but it's still an unGodly high marginal tax rate.