Why do some people prefer ratifying conventions, rather than state legislatures, for the ratification of amendments?

People believe that conventions created specifically for the ratification of amendments form better representations of the people's will. State legislatures can oftentimes be biased for or against a certain amendment for their own wellbeing rather than that of the people they represent.

One major historical example of this can be seen in the use of ratification committees for the ratification of the American Constitution; the Founding Fathers believed that certain state legislatures would not ratify the Constitution even if the citizens of the states wanted to, so special conventions were created to more accurately portray the will of the people.