Why do you think the framers of the constitution required a 2/3 senate majority to remove executive and judicial branch officials

The principle behind it is the "separation of powers" - the principle that no branch of the government should heave absolute power in their hands, so that they can't abuse it.

Only if the congress is very sure that the officials in other branches need to be removed - and this "very sure" is measured by requiring a 2/3 majority, can they remove them 

Ataxation measure enacted to raise revenues for a standing british army in america