Several people have requested this, but it is a feature that only a small percentage of players want. For that reason it is a little low on the priority list, however your request is not unheard.
The reason attacks are a bit slow when you start is so that attack speed can feel like a valuable upgrade. Along with that it allows you to have one hand free(for obvious reasons). If I add a mechanic to manually attack then attack speed as a mechanic will have to be reworked into a cooldown, or done away with entirely.
In time, (probably near the end of development) I'm heavily considering adding manual attacks as an optional way to play, but as of now I don't plan to implement it anytime soon.