Because, ionic compounds are not like covalent compounds which have localised attractions between two positive nuclei due to a shared pair of negative electrons. Ionic compounds have positive and negative ions. read more
If you mix multiple ionic compounds in solvent, a melt, gas phase, the original paired associations are spontaneously scrambled. Benzene plus xylene does not give you toluene. "Separating" benzene is not electrostatic attraction. read more