My theory...
Carl Horner did not have a nice formal studio shot of Matty to use for the large Horner composite which is pictured on the postcard.
All Horner had to work with was this odd photo of Matty with a hat which would have looked really out of place in the large Horner composite (as it does in this picture).
Matty had his early formal studio picture taken by Ben Falk (not Horner) before visiting Carl Horner later in his career.
So it's not about not making the cut as a player, but not making the cut as a photograph.