In the source code for keymaps, there’s this piece of code:
;; These are only (?) used in contexts where there is no text field
;; interested in the actual typable input.
(def ^:private default-allowed-typable-shortcuts
#{"A" ; :add
"E" ; :rotate-tool
"F" ; :frame-selection
"R" ; :scale-tool
"W" ; :move-tool
"Shift+A" ; :add-secondary
"Shift+E"}) ; :erase-tool
To my understanding, the reason for this seem to be that the keymap I opened up to customization seem to work globally, even when in a text field. While commands that can be interpreted as text (e.g. “A”) can’t be global hotkeys, since then you wouldn’t be able to type those characters.