It's not easy standing in front of a crowd, having two hours at your disposal and needing to make the best of it. You don't know exactly how each person in the audience will react to you - hopefully positively! - but you will rehearse and get better at your delivery. Some cynical looks, some semi-interested, some asleep.
Just like stand-up comedy, so I think. Those guys have it way harder, because they're trying to make people laugh and humour is so subjective.
Every time I teach, I learn even more.
I just wish I didn't get a sore throat after every lesson because of a very passive (more like shy and don't know what to ask because no time to do readings) crowd.