One possible answer is Americans don't know the Constitution and think education is more important than exercise. Thus, Congress has authority to pass laws dealing with the more important areas of our lives. Another possibility is Americans have contempt for the Constitution and its limitations on Congress. They see strict constitutional obedience as an extremist plot that will prevent them from forcibly imposing their vision of the good life on others. No speculation is required.
Most congressmen are lawyers.
More than any other segment of our society, lawyers have the greatest contempt for constitutional principles and rule of law. But there are many congressmen who are not lawyers. Most of them believe most anything is permissible if they can summon a majority vote. There are a precious few congressmen who actually understand and respect the Constitution's limits on federal government. They don't protest impermissible acts of Congress because is they fear for their political lives.