What would be the reasons for not having Jokers in a deck?
In my experience, the vast majority of decks do in fact run Jokers.

The main exception is a deck that does not want to get into shootouts at all or make any pulls. This is typically a "Landslide" deck that focuses on playing more dudes &amp; deeds than the opponent can deal with.  It often includes cards like Make the Smart Choice or Pistol Whip, seeking to remove everyone from a posse before it ever gets to comparing Draw Hands. In such a deck a Joker will be a dead card if ever drawn to your Play Hand so there is no point in including them at all.