The United States Constitution places no time limit on the terms of Supreme Court Justices mainly because: the framers wanted to ensure that Justices should be free from political or economic pressures.
By granting lifetime appointments, Justices can make decisions based on the law and the Constitution rather than worrying about re-election or pleasing a particular political party.
This independence helps maintain the balance of power between the three branches of government and preserves the integrity of the judicial system.
In short, lifetime appointments for Supreme Court Justices were designed to promote impartiality and protect the judiciary from external influences.