That is what I thought. Pretty crazy that there is not some sort of phase out for this.
Each additional dollar you earn is taxed the same way for everyone. I think it makes sense. You want the tax rates to be predictable for people. And if you suddenly had your first $90k become taxable because you hit a certain threshold, then you might have a tax rate far exceeding 100% for that next dollar of income.
That would be the point of a phase out, instead of a tax-cliff. Not all $90k would be taxable all at once. It would probably look something like the method employed by the US Corporate Tax code, which increases taxes once you get past a certain threshold so that all income is eventually taxed at the top marginal rate.
Taxable income over Not over Tax rate
$ 0 $ 50,000 15%
50,000 75,000 25%
75,000 100,000 34%
100,000 335,000 39%
335,000 10,000,000 34%
10,000,000 15,000,000 35%
15,000,000 18,333,333 38%
18,333,333 .......... 35%