Why do hockey players get into fist fights the majority of the time during a game?

Tradition.

Avenging an infraction against a teammate, especially a skill player or goalie.

To get their team fired up if they?re sluggish or losing.

Frustration.

To prove how tough they are.

Because it?s not prohibited or significantly punished.  If there is
nothing other than a on-on-one fight, each player gets a 5 minute
penalty and the teams go back to playing at even strength.

Because the fans like to see it.  

Boys will be boys.  It's a physical, confrontational, full-contact
game played by big strong men.

Just a bit of editorial.  I?m a big fan of hockey at the NHL and minor
pro, junior and college levels.  There are fights in the men?s games
in all of these leagues.  The first time I saw women play hockey I was
amazed and disgusted at the number of times the women slashed and hit
each other with their sticks, especially in the head.  Cross-checking,
tripping, and slashing were all rampant.  I think this is because they
didn?t have the traditional outlet of body-checking and the occasional
clear-the-air fight as in men?s hockey available to them.

I am afraid it is partly because the fans like it  - sort of like
watching race car events.  Those can be pretty dull (hockey is not!),
and crashes add thrill, especially now when  - thank goodness -  the
driver usually can walk away.
I wonder if the hockey players get a bonus for a fight that doesn't
affect the score???

"Why do hockey players get into fist fights the majority of the time
during a game?"
They don't, the clock is stopped.  You probably mean - in the majority of games.

Ever hear the joke about the guy who went to a fight and a hockey game broke out.