Why do ionic compounds tend to have higher boiling and melting points than molecular compounds have?
Well, look at the molecularity of an ionic species compared to a molecular species.
Ionic species are essentially non-molecular with NO molecular boundaries. Given the fact that there are no discrete molecules and strong electrostatic interaction between ions it takes a lot of energy to disrupt the interaction, and this manifests in high melting and boiling points.
See this old answer.