Yeah, this always weirded me out from a integrity and game perspective whenever I hear about this as there's not really a good solution.
There's a few scenarios when someone disconnects, but here's the main ones: Could' be a unexpected event that forced them to run, a rage quit or a actual disconnect. You can't really tell what it is during the game as you can't use a engine to check the game of course. So how do you know if the opponent figured out if they found out they were losing and rage quitted? Therefor the thing that makes the most sense is to pick the draw. If you see a win, then I guess you'd pick the win option. But that's only from a integrity perspective because as people showed, they may just pick the win anyway. Which... May technically be correct in the next section based on how game rules tend to be. See...
From a game perspective: Even in person tournaments, not just chess, will award the victory to the one who shows up or stays in the game. Like, say... If someone angrily leaves the place and doesn't tell anyone. Heck, that's even the case in the really rare but unfortunate occurrence of dying like a fairly recent example of Emory Tate:
www.chess.com/news/view/emory-tate-1958-2015-7615 So the rules of games necessitate a loss in such cases because there's no way for the game to go from there. I mean how would one tell the actual outcome? If it's called a draw and you don't get full points, you may not be able to win the tournament. Yet you can't really say something is a "win" or a "loss" either because those don't seem accurate since the game is unfinished and someone can flub any time.
I've seen some games have a "abandonment" sort of thing where it's still counted as a win "point" for the one still in the game, but not actually a win for the game itself. That seems to make more sense because of said tournament point issue but also classifying the game into a different category of being inconclusive.
But then there's another layer on top of it that leads to the rating part: Does it make sense to change player rating based on the end result of the game? It's harder to judge this because you can't calculate rating based off of a game that wasn't finished. So it would make the most sense to just not change the rating in regards to the game. But what happens if people abandon games just to "punish" their opponent that they rage quitted on? As noted above with online play, it's way too hard to tell who is doing that on purpose. So I guess they have to do some rating distribution as well otherwise people can abuse the system to avoid losing their own rating points in losing positions. Is it right if someone actually lost connection? Nope. But unless there's some way to tell for sure, it's just something that players have to live with I guess. It may not matter much in the long run though because with rating based pairings you are bound to win back the points you lost and lose the points you won. Plus ratings fluctuate anyway.
It would suck if it just so happens to be out of range of some rating barrier to entry in a tournament though. Like if someone was 2010, loses 11 and goes to 1999, then can't enter a 2000+ rated tournament in time because they just got back online before the tournament started and couldn't play a game or two in time to get it back to enter. But that would be a really rare situation.
So I don't think there's a perfect solution no matter how you slice it. But I could be wrong as perhaps there will be some way to figure it out one day. Though this has been a gray area for as long as games (and ratings) existed so I'd be surprised if the solution was found soon. Like even if you could tick a box that marked the game as unfinished or abandoned instead of a hard W/D/L, that still wouldn't solve the prior things. Like if marking a game unfinished/abandoned reduces or eliminates rating point losses for instance, that would still unfortunately be beneficial to people who purposefully abandon games because they'd lose less in the long run. Though maybe it would still equalize eventually anyway because you can't cheese holding a rating forever similar to it being impossible to keep your rating perfectly steady or at your highest at all times.
