why are most of the covalent coumpounds insoluble in water?

Covalent compounds lack the property of dissociation, and as a result, most of them are insoluble in water.

However, the polar covalent compounds are easily soluble in water as HCl, HNO₃, H₂SO₄, Glucose and most of the sugars, Sugar has many polar covalent bonds, in the C-O-H groups, and the molecules of sugar fit easily into the hydrogen bonded microstructure of liquid water.