Perhaps you're missing context here? The US Congress has established and frequently reaffirms a policy called the "debt ceiling", which requires the government to default on some of its obligations (including debt repayment) soon after reaching a certain nominal amount of debt. In 2023, negotiations to increase this ceiling lasted up until the week before the default would have begun, and 36 Senators still wanted to reject the deal and force the default. To me it does not seem insane or irrational to worry that next time there might be 41 Senators who want to default.