This is only the case because investors are willing to buy treasury bonds and loan the money out at those levels. If things get worse(though no one knows where the line is) and they will, at some point those investors will wisen up and demand higher interest.

These rates are abnormal rather, go back 30-40 years and if the rates got anywhere above 5% (which are still incredibly low) it would crush the servicing of debt and cause runs on the system.