You may not have encountered it yourself, but there is actually a punishment, it doesn't kick in until the 3rd game or so that you've left without playing. It starts at 5 minutes then if you do it again 10, so on so forth until some cool-down timer kicks in and after that you have 3 games again.
I'm then confused how I see it so much. Because the frequency it occurs would indicate zero repurcussions
That said, I can also see the math that this delay on the timer doesn't work. If you have a 20% chance per game of being imposter....
Game 1: 20% chance. If not, you leave (80%).
Game 2: 20% chance. If not, you leave (64%)
Game 3: 20% chance. If not, you leave (51.2%)
Based on that, a habitual leaver will get imposter before the timer kicks in basically 50% of the time. They'll then play through the game, and reset? their timer, allowing them to repeat
And the other 50% of the time, they just go play other games instead, having ruined 3 games for up to 9 other players each.
There shouldn't be a "3 game" trigger. It should occur the first time you leave, period. You're free to rejoin the game you left, but otherwise you have to wait for it to finish.