Because lipids are primarily composed of long chains of carbon and hydrogen bonds (hydrocarbon), the low electronegativity difference between the two atoms result in a non-polar bond, which is the opposite of what water molecules are composed of, which are polar bonds (H-O).
Good solubility is when the molecules of the solute are easily attracted to the molecules of the solvent. Since polar molecules have electrically charged poles on different ends of their structure, they will attract other poles from other molecules i.e. polar molecules.
So to simply put it, non-polar solutes are not soluble in polar solvents, but mainly in non-polar solvents.