You don't have to be a WWE wrestling legend to become the undertaker. Funereal work is one of the most somber professions known to man. You're dealing with human remains, grieving relatives and difficult family occasions. It takes a special person to be able to cope with the stress and sadness that a role like that can bring, and it's no surprise that not a lot of people want to do it.
It's a specialist job, and one where demand is constant. Because there's a lack of funeral workers, most towns and cities don't have enough funeral directors, and that lack of competition means prices are high. The average funeral worker earns something in the region of $60,000. You can imagine how much more you'd likely be earning if you managed such a place yourself. So long as people keep dying, there'll always be work available.