Arguably it makes a little more sense for keyboard layouts, but even then.
Edit: also with alternative layouts. Is Dvorak English? If you want you can create your own keyboard layout with Ukulele https://software.sil.org/ukelele/ (or edit an existing one) and change the icon to any image.
Two-letter icons also don’t help with alternative layouts. Flags are useful for e.g. US English vs. UK English, but are bad when a country has more than one official/widely-used language (e.g. Canada) or when multiple countries share the same keyboard language and layout.
It doesn't just use two-letter icons. The Arabic layouts show “ع”. The Hebrew layouts show “א”. The Greek layout shows “λ”. The Thai layouts show “ก”. The Canadian English layout shows “CA”, the French layout shows “FR”, the Canadian French layout shows “CA” above “CSA”, and the Swiss French layout shows “CH” above “FR”.
Arguably it makes a little more sense for keyboard layouts, but even then.
Edit: also with alternative layouts. Is Dvorak English? If you want you can create your own keyboard layout with Ukulele https://software.sil.org/ukelele/ (or edit an existing one) and change the icon to any image.