One of the biggest hurdle when starting a new mmo is to setup the inputs in a familiar way. We are usually already used to play other similar games so being able to setup inputs in a similar way makes it easier to get into a new game. Minimizing friction is very important to enroll new players into a game, especially in a relatively niche genre where you want to enroll players who already built a lot of habits in other similar games.
I happen to have a possibly somewhat unusual setup, where I want to perform all movements with the mouse, and all actions on the keyboard. This usually implies using the mouse button(s) to move forward. But in crowfall, I can't because the mouse button is arbitrarily marked as "reserved", aka "I am not allowed to bind something else on it". I don't understand why.
Likewise, since I'm left handed and use the mouse with my left hand, I typically want to use the right most part of the keyboard for abilities. The layout of the keys over there can be a bit awkward but the presence of some very large keys such as backspace and enter typically makes up for it, by allowing me to use those large, easy to reach keys for important abilities.
But again, I can't reassign them. "enter" is also reserved. I am usually happy to use shift + enter to open the chat so I can use enter for something else, but I am not allowed to do that.
The purpose of allowing people to customize keybinds is to let people setup things in ways you haven't anticipated. So I don't see the point of arbitrarily limiting it in this way.
I can still have the setup I want, by reprogramming my gaming mouse buttons and my gaming keyboard keys. It's just a big and completely unnecessary pain point.