There is a difference between playing against the house or a computer and playing against other players. I cannot judge which one is more fun though. There are people who find it more fun to play alone while there are also people who find it more fun to play against fellow gamblers.
It is not just whether a person is introvert or extrovert. It might simply be just a matter of mood.
True, I do single player games when I don't want to talk or socialize or play with other gamblers but I do play a lot of multiplayer games too, sometimes I play multiplayer if I'm in the mood to be competitive with other gamblers. It will also depends on what games are we talking about too. Most of the times, I play single player whenever I'm in bed before sleeping, too tired to talk and interact or to think too much, I'm just playing to waste the time before going to sleep so I'm used to playing by myself.