Don't you think teacher want to explain mathematical theories practically?

Sure with no doubt, Any kind of science needs this practical reflections.. so imagine if it was about mathematical theories. 

Without a doubt, in order to consolidate the theory in the mind of the student.

The good teacher should explain why do we study the mathematical theories and concepts and where they are using (with an example)

Surely.  Most of the time it is needed in mathematics for better understanding of topic by students.

yes, it is easier to understand 

Yes, Teacher's do want to explain the theories practically. This makes the concept more easy for the students