There are no answers to such why questions, in case anyone is looking for an "answer". Although it is very tempting to rationalize every laboratory observation, there are no definite answers to questions about why certain chemical phenomena occur. While it may be tempting to come up with explanations that allow us to pass exams or understand concepts on a surface level, the truth is that our current understanding of chemistry is not advanced enough to accurately predict the solubility of compounds in water or other solvents. The same goes for melting and boiling points. Tools such as ChemDraw and SciFinder can provide estimates, but there is a significant margin of error in those solubility numbers and the results may be incorrect.
Let us see the complications, e.g.,
Take anhydrous $\ce{MgCl2}$, add it to water and dissolve, the reaction is exothermic, and solution can be shown to be slightly basic.
Take the hydrated version, $\ce{MgCl2.6H2O}$, and add it to water, the reaction is not exothermic in water, and water's pH does not change. So may even ask, which magnesium chloride is being discussed?
As a result, many chemists rely on macroscopic measurements such as thermodynamic properties but such properties are quiet about microscopic details and "whies". A paper titled The solubilities of some inorganic halides, Trans. Faraday Soc., 1958,54, 34-39, is relevant the OP's question with actual experimental data. The abstract reads,
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They have the thermodynamic data of Group I and Group II halides in Table 1.