Researchers simply follow their training and use the method that feels most comfortable. But two other factors also influence the choice of method. One of these involves the scholar’s philosophy of science as it favors one or another method of gathering and presenting information.
The other reason has to do with the practical limits on the way researchers can operate; strategies vary in the amount of control required of the researcher. Sometimes qualitative research emerges as the most or only feasible method, given the nature of the subjects and their environment.