What you're suggesting is that teaching comes down to having good presentation skills and the ability to entertain. Sure being able to put forward ideas in a way that doesn't send students to sleep is important but they are not the only traits a teacher should have. Ultimately an entertainer is more concerned with themselves and their performance whereas a teacher puts their students first and seeks ways to get the most out of them. To do this in the field of ESL a teacher needs to allow his or her students to take centre stage, encouraging them to interact and use the language as much as possible. While a teacher may often provide the initial topic and/or stimulus for a discussion they should also know when to step back, mediate and observe - not the sort of thing most entertainers do in their day to day jobs.