[Sivart13]

In an effort to keep the scope manageable for the pilot year, the Direct File team chose to have an upper income limit so they would not have to support Form 8959: Additional Medicare Tax (https://www.irs.gov/pub/irs-pdf/i8959.pdf) which only kicks in at that threshold.

Though it's also very likely at these high incomes that you would be disqualified for other reasons (investment income etc)

[MarkSweep]

8960 (net investment tax) is another form that only applies at 200k or more income.