alkali n alkaline earth metal's periodic trends

[cracked_doc]

Now I don't understand this : in the alkali and alkaline earth metals first they say that the solubility of their oxides increases down the group...then they say that the solubility of their hydroxides also increases down the group. this is because lower members have lower lattice energies so they dissociate easily and dissolve in water...

But they say that the solubility of their carbonates and sulphates decreases down the group....WHY??...it should also increase following the above reason they have given......thanks for hlping