The 10th reason isn't very scientific, but it's possibly the most important. Being a pro speaker is fun!
Of course, as in any business, you have bad days to go along with the good days. But as pro speakers will tell you, the good times far outweigh the bad.
It all comes down to this — life is short, and you spend so much of it at your job. Shouldn't you be spending all that time doing something that you want to do?