They wanted judges to make decisions based upon the law and not public opinion.
Explanation:
If the judges were there until they retire then they could be more objective. That is because if they had to be reelected, they could just support what the people want so as to get reelected, which would mean that they are not objective and lawful judges.
Framers were well known that judges must accountable to the people at all times. The reason behind their action was as framers were feared of victimization from the judiciary more than from the rest of the two branches, so they placed limitations intentionally on the judiciary.
