A legal permanent resident must wait five years to be eligible for U.S. citizenship. This is reasonable: one must demonstrate his/her intention to permanently live in the United States, and that he or she has good morale characters. This requirement gives government officials some time to evaluate a person.

Having said that, however, isn't living in the U.S. for many years pursuing a green card an even better demonstration of those purposes?

For a person who enters the U.S. with an immigrant visa, thus becoming a permanent resident upon entry, it is understandable why s/he has to wait for 3 or 5 years before s/he is eligible for naturalization. But if a legal nonimmigrant spent 10 years in the U.S. patiently waiting for a green card, paying taxes and never having trouble with the law, why is the 5-year residence requirement still necessary?