why are strong acids and strong bases not titrated ?

One of the most common titrations done in chemistry is the titration of strong bases against strong acids , and vice versa. I cannot imagine where you get the information that this does not happen. Perhaps you would like to provide a little more information on the background of this question .
I am sure that you have seen the equation:
NaOH + HCl → NaCl + H2O .
This is a strong acid / strong base titration

What is very uncommon and discouraged is the titration of a weak base by a weak acid.

They tend to be less interesting in their chemistry than when a weak is titrated with a strong. For example, you can use the pH at the half-equivalence point to determine the Ka. This is not a calculation possible when strong is titrated with strong.