If someone is primarily earning their living from speaking, they're probably pretty good (or have a particularly compelling story to tell)--or they wouldn't be earning their living from speaking. As the parent suggests, most people in, say, the tech industry give talks at conferences etc. now and then as a sideline. Some more than others, some better than others. But mostly, they're not having coaching, watching video, rehearsing extensively etc.--i.e. the things a professional athlete does all the time. They're just going out and doing it at least well enough that they get invited back.