Why do they call for my services? After all, these are great individuals in their own rights. They are amazing people and all have accomplished or are accomplishing great feats. The answer is very simple.
They are smart enough to realize that only because they are great at their profession, have a successful business, a great reputation, have connections, have a winning idea, a successful story to tell, or have had a successful string of businesses in the past, that not of this will automatically mean that they have refined their skill of Presentation and Speaking to a World Class Level.
Like every other skill, Public Speaking requires you to get the right knowledge and training in order to achieve the results you desire and win.