##Actually, 18 bytes

    5Pτ;r;∙`MúE`M╪k♂Σi

[Try it online!](http://actually.tryitonline.net/#code=NVDPhDtyO-KImWBNJ0FPaStjYE3ilapr4pmCzqNp&input=)

-4 bytes from Leaky Nun, and the inspiration for 4 more

Explanation:

    5Pτ;r;∙`MúE`M╪k♂Σi
    5Pτ;                two copies of 26
        r;              consume a copy for range(26), duplicate that
          ∙             Cartesian product
           `MúE`M       for each (x,y) pair:
            M             maximum
             úE           element in lowercase English alphabet
                 ╪k     list of length-26 sublists
                   ♂Σ   concatenate strings in each sublist
                     i  flatten and implictly print the stack