aqueous solution - Why do some insoluble salts undergo slow chemical reaction instead of dissociation in water?

$$\ce{PbCl2 + H2O ->[\Delta] Pb(OH)Cl + HCl}\tag{1}$$ $$\ce{2ZnCO3 + H2O ->[\Delta] Zn2(OH)2CO3 + CO2}\tag{2}$$ $$\ce{2NiS + 2H2O → Ni2(OH)2S + H2S}\tag{3}$$ $$\ce{Hg2SO4 + H2O → HgO + Hg + H2SO4}\tag{4}$$

The above salts are all insoluble in water. Even in the saturated solution, their concentration of salts is very low. They are expected to undergo complete dissociation in water due to their low concentration.

$$\ce{insoluble~ salt <=>[water] constituent~ ions}$$

For e.g. let's take lead chloride:

$$\ce{PbCl2 <=> Pb^{2+} + 2Cl^-}$$

$\ce{K_{sp}}$ = $\ce{[Pb^{2+}][Cl^{-}]^2}$ = $\mathrm{1.6} \times 10^{-5}$

From the solubility product value, we can determine that lead chloride is insoluble in water. But what about the reaction above with water? Since, they do not dissolve in water, they do not react with water in any way except dissociation. So, can the reactions be neglected? Or should it be considered occurring while the salt is poured in water?

source :- reaction 1, reaction 2, reaction 3, reaction 4