One of the following statements (at least) is therefore true;
1> You're not actually telling the truth, for whatever reason
2> Those people are idiots who don't understand how tax brackets work, and are basing their decisions on that gross ignorance, and refusing to learn how things actually work, or
3> They'd be losing money due to loss of support programs, which is admittedly an issue in the USA as incomes climb, but is an issue entirely separate from taxation.