I'd like to understand the reason behind this. Why wouldn't enemies have this same restriction?
I can't really speak to specific boss attacks having this as I haven't done much boss fighting, but it doesn't exactly seem balanced that a Sentinel can attack with a halberd at range 0, but a player can't. I understand that enemies are controlled by behaviour cards and not players, but they have the same action limitations as the players.
If I remember correctly from the video games, enemies with lootable weapons had the same moveset for that weapon as players did, so the above restriction doesn't seem to translate properly either.
Although now that I write that, perhaps giving players an increased moveset but restricting range, while giving enemies a limited moveset but increased range is their way of balancing?