Rebinding mouse attack key action to a keyboard prevents from sending constant "attack" action

if you keep your mouse left button pressed you can mine blocks which you can mine instantly with a tool very quickly. However if you rebind that action to a key on a keyboard - you can only mine blocks once in a while.

Also - if you aim at the air, pressing a mouse key doesn't involve having any extra animations, but doing the same with a rebound keyboard key - keeps "reloading" a tool every half a second or so.