Answer:
Convention method is seldom used because it is considered controversial.
Step-by-step explanation:
One of the methods of proposing an amendment is by a "two-thirds" vote of each house of Congress. This is the most popular method used till date.
The other method for doing this is by a national convention. But this has only be used twice till date and is considered controversial. This is because to bound to one amendment, such convention is not required. In 1970, President Jimmy Carter also cautioned that such convention can become uncontrollable completely because legal scholars can propose amendments on any subject.