Why are +2 oxidation states more stable for tin and lead than for carbon and silicon?

The tendency for elements in the carbon group to favor the +2 oxidation state over the +4 state increases as the atomic number increases.

While carbon and silicon are very stable in the +4 state, the heavier elements in the family exhibit a growing inertness of the $n{s}^2$ electron pair. These electrons are closer to the nucleus than the $n{p}^2$ electrons and become increasingly difficult to remove as the atomic number rises. This phenomenon, often referred to as the inert pair effect, allows the $n{p}^2$ electrons to be removed separately, facilitating the formation of +2 ions in elements like tin and lead.

Consequently, while carbon and silicon do not form stable +2 ions, tin shows roughly equal stability in both +2 and +4 states, and lead is dominated by the +2 oxidation state, with only weak tetrapositive properties.12