On what basis are you making such a statement? There are quite a few types of masks, which of them protect 70%? How did you check or who checked the 70%? In my opinion, this is almost impossible.

It is very difficult to assess the effectiveness of the protection of masks, too many other factors can affect the infection of a person. It would be more correct to say that we do not know how much the masks protect us.
Moreover, the main infection is probably through the eyes.