Extemporaneous speaking should be practiced and cultivated. It is the lawyer's avenue to the public. However able and faithful he may be in other respects, people are slow to bring him business if he cannot make a speech.
But HBO is less interested in how many people are watching than in how much the people who are watching are liking the show. They didn't set up their business model to make writers happy. It's just a nice unintended consequence.