There are two types of fears that stem from the same source- communication. One is the fear of the insane and the other is a fear of respected people.
In my naive opinion I feel there is no reason to be afraid of robbers, criminals or any other such harmful people , so long as they are sane. If a person has a brain that is working I feel there is hope to communicate to them not to commit their evil act and escape freely. However, if the criminal is insane; mentally ill, then they are just as much dangerous as any other mentally ill person. Since they can not communicate properly. Their brains aren’t functioning so you can not convince them not to harm you.
Now, respected people can be completely sane and usually are since they need power and intelligence to be respected. However, because of the need to respect them they have an aura of fear around them. There is a disturbance of the ability to communicate with powerful people.
One such respected person can be a teacher. Teachers always tell parents at PTA that their children are excellent good kids, the trouble makers are exceptions. Now why is it that kids behave so well in school while at home they can be misbehaving. It is because in school children are taught to respect their teachers, they are afraid to be absent or late for the consequence. A child can be able to give a whole review lesson to its classmates before the test. However, when it comes to giving a speech in front of the class with the teacher there, it can become impossible. There is a fear toward the respected teacher.
That could be why we have to fear G-d, it signifies our respect. Among our peers, friends and families it may be easy to communicate since we are all on the same level. You don’t have to prepare a speech in advance, it just comes out naturally. Now, one can appreciate the power of Tefillah, of having a Siddur in front of you with all the words written for us.