My concern with binds is that if someone was allowed to bind say overheads or even just stabs, that would theoretically give them an advantage. You can make your whole game about stabs and mixups with stabs included. So, if I could bind say just my stab key, that would make it much, much easier to combine up, left, or right attacks with my stab. But the defender has no such advantage. Sure theoretically you could have a stab block key, but you could also theoretically have a right swing + overhead keybinds and use those in combination with footwork to create a really good strategy and ultimately you'd need those defensive binds to ultimately counter it.
It could very well lead to a meta of binds, which would be fundamentally bad in my opinion.
Example. Let's say binds were added. I add a stab bind to my mouse 3 button. My game is to feint left, overhead, and then hit my mouse 3 bind while im looking up to drag a stab down on them. Because of my mixups, i'm causing my opponent to look up naturally to defend the overhead that i've established. But when they adapt to this is when I do my "looking up" stab to take advantage of the fact that most players use the default setting (hypothetical example). That could lead to players opting to have a stab block or downward block bind. In the end, it could very easily lead to a situation where there's a "best" bind loadout, and if you don't have it you can't compete.
As I said above,I dont know that this would be the case, to assume so would be presumptuous. But if you added binds, the pandora's box would be open and if it DID turn out to be a problem, many people would be very upset if it was removed (loss aversion).
Hope that makes sense.