Among the alkali metals why all other metals except Li and Na can form super oxides ?

Explanation

The peroxide ion , `overset(Theta)(O) - overset(Theta)(O)` (which is probably generated first by transfer of electron from the metal atom to molecular oxygen ) is unstable in the presence of small positive ion like `Li^(+)` with a high enough charge density . When `Li^(+)` comes close to the peroxide ion , electrons in the peroxide ion are strongly attracted towards the `Li^(+)` ion and as a result , the peroxide ion breaks down into an oxide ion `(O^(2-))` and oxygen atom `Li^(+)` ion breaks peroxide ion `(O_(2)^(-))` even more easily .

The very small `Li^(+)` ion with much higher charge density readily combines with the very small oxide ion `(O^(2-))` with much higher charge density to form a very stable lattice (a thermodynamically favourable process ) of the normal oxide `Li_(2)O` .
Large `Na^(+)` ion with moderate positive field around it cannot break the peroxide or superoxide ion easily . In fact `Na^(+)` ion combines with the peroxide ion `(O_(2)^(2-))` with moderate negative field to form mainly the peroxide `Na_(2) O_(2)`
Very large `K^(+) , Rb^(+)` and `Cs^(+)` ions with very low charge densities are completely unable to polarise and break the peroxide or superoxide ion . They actually combines with the superoxide ion `(O_(2)^(-))` with a much weaker negative field around it to form superoxide `(KO_(2) , PbO_(2) , CsO_(2))` . Also the formation of such superoxide in thermodynamically favourable compared to the formation of other oxides .