Disconnecting from a match is harmful to the team. Community requested punishment for leavers, and that's what was implemented. You still get rewards win or lose, but not if you leave.
Like take this example:
https://www.youtube.com/watch?v=7UmU4mPvKco I was being friendly because it was a team of almost all new players. Level difference be dammed, I'm a skilled antagonist and would wipe them out in a couple of minutes and may make them ragequit. I used to not care but now that I do, I wanted to help.
One player STILL disconnected in the middle of the mission. And then because of that, the extraction timer at the end was waiting on that player to come back, and it was an incredibly long timer due to a powerful antag making the game easier and more forgiving for the Raiders.
Because it was so long.... the OTHER level 1 got tired of waiting and disconnected, rather than just wait and get their rewards. They already extracted, they already won, but 1 player hurt the experience of everyone else and added 3 minutes onto the end of the match.