No reason, I always thought launching pinentry directly chose the right one out of pinentry, pinentry-curses, pinentry-emacs, pinentry-gnome3, pinentry-gtk, pinentry-qt, pinentry-tty since it always worked for me on xfce+arch+programs I have used.
You can change it I suppose, I don't thing I use gpg-agent often.
You can change it I suppose, I don't thing I use gpg-agent often.