Here's why:

* Bonding: Nonmetals typically form covalent bonds, which are weaker than the metallic bonds found in metals. Covalent bonds involve sharing electrons, while metallic bonds involve a "sea" of delocalized electrons.

* Intermolecular forces: Nonmetals often have weaker intermolecular forces (like van der Waals forces) holding them together in the liquid state. These forces are weaker than the metallic bonds in metals.

Exceptions:

There are some exceptions to this general rule:

* Network covalent solids: Some nonmetals like carbon (in the form of diamond) and silicon dioxide (SiO2, quartz) have extremely high boiling points due to their strong network covalent structures.

* Diatomic nonmetals: Diatomic nonmetals like nitrogen (N2) and oxygen (O2) have relatively low boiling points because they are held together by weak van der Waals forces.

In summary: While there are exceptions, in general, nonmetals tend to have lower boiling points than metals due to weaker bonding and intermolecular forces.