There are just SO many reasons why people do it and while sometimes it bugs me too, I've done it for good reasons..
Teammate gets kicked from game before it starts. You back out to join their group again.
Other team is full of humans, while your team has half that number.
If it's drop-in then the other team is CLEARLY a club and you're playing with all randoms and your goalie is a low level guy, likely playing for the first time.
You recognize a name on your team because you have a mental and physical list of the trolls in the game.
Other team decided it would be cool to use white sweaters at home and now you can't tell who is who because you didn't catch that fast enough.
Your ping is outrageous and lagging too bad to want to continue trying to play to hurt your team worse. This is especially the case if you're center, losing EVERY faceoff.. playing a team in Montreal on their servers haha!
If I got a 30 min ban for any of those I'd be pretty salty.. but then I do hate when people back out just because they're down a goal or 2 or they see the other team MIGHT beat them so they continue searching for a team they're more confident they can beat.
If you look at eliminator stats sometimes it's funny. A team will go 60-0 but they will have 30 rd1 wins 20 rd2 and 10 finals wins. Why? Well because they were about to play a team that MIGHT beat them so they'd sooner quit before puck drop and start up a new tournament to play a team they are more sure they can beat. If it's off by 1 or 2 then likely someone failed to advance so they forfeited tourney or they had to do something, or someone got on.. but if it's wildly skewed, then you know they are picking who they play just to boost their w/l record.