A lot of US benefits have “benefit cliffs” where making $1 more substantially reduces or even completely disqualifies a person from programs like SNAP (food stamps) or childcare subsidies or Medicaid. https://www.ncsl.org/human-services/introduction-to-benefits-cliffs-and-public-assistance-programs

It’s not surprising people whose families are directly affected by, or who know people affected by, benefit cliffs think the lawmakers set up taxes the same way.