Covalent bonds are between 2 non metals, which causes their electrons to be shared. Since they are shared, there are no bonds to be broken between them which causes them to be easier to separate. Thus, they have a lowing melting point.
Ionic compounds are between a metal and a nonmetal. In this type of bond, electrons are transferred from metal to nonmetal. Ionic compounds have very high melting points because they do have bonds that are extremely tight and close together, making them a lot harder to pull apart. So the higher the temperature, the easier it is to pull the tights bonds in an ionic compound apart.