Why don't they put a ban on manufacturing of weapons if governments all over the world want peace?

The ban on manufacturing of weapons cannot be put and is not practical at all. This is because weapons are required for both defense and for internal security. If there are no weapons left in the world, crimes would still be committed although with stones and swords instead.

Hence, for the safety of a nation both in terms of internal stability and to deal with the external threats, manufacturing of weapons is of extreme importance. This is the prime reason why governments all over the world do not put a ban on the weapons simply because it is neither applicable nor practical.