This is a question I have never encountered before, nor any type of it. I will try my best to answer it though.
Famous speeches normally become famous because they have said something that has affected the audience emotionally or even physically. Normally, most famous speeches I know of are quite lengthy and feature quite complex words and they are meaty pieces of text. So, learning the speeches might give said person an emotional view to it as well as an accomplished view on the hard piece of text they have just memorised.
I hope this helped. ;3
