Why is it a good idea to make interest payments for those loans that accrue interest during a grace period?

Because during the grace period interest will accrue and it is added to the principal which also accrues interest, increasing your total debt.

Explanation:

A grace period refers to a period of time in which you are not obligated to make payments. However, some loans provide a grace period but interest accrue which increases the amount you owe. Because of that, it is a good idea to make interest payments on those loans to save money by avoiding that the interest is added to your principal raising your total debt.