No. Just… No.
There is no reason whatsoever to punish those forfeiting, especially if not done abusively.
You are solely wasting your time and the time of your opponent when you know for sure you cannot win no longer and keep on going nonetheless.
The only possible aspect that might annoy you, maybe, is that you earn less experience points and they might forfeit at the very moment the game is making them pass anyway in the decisive turn, for some obscure reason, which might be perceived as rude, rather than wait the few seconds it would take for the game to do its things on its own.
No matter what, there is no reason for you to get upset.
In the first case, you might have loss a few experience points on Performance scale, but save some time in the process ; it adds up at the end in a clear experience gains.
In the second case, well, it might be annoying, but I am sure you are capable to deal with it in a reasonable manner. There are multiple reasons they might want to forfeit at that moment, chief among them not wanting to waste time looking at the game doing its things where it makes both players pass and other things of the sort. Some other reasons might include a fluctuant Internet, pushing you to rack up the most games quickly when it works fine. I had, for once, had won a game, but my Internet was so shitty at times that I was forced to forfeit despite the fact I had already won ; both players had no more card in hand, I had a higher score. All was great. Then, the game proceeds with its procedure, but before it could do all its stuff, my Internet crashed and I was forced to forfeit. I lost the game despite having taken the time to win it. So, it might push some to take advantage of their fluctuant Internet. The point being : I do not know. I have no control over them, and I am sure they mean no harm to you. In the contrary, you have control over yourself, though, and how it affects you.
In any case, you cannot know if they do or do not learn as much as you do from the match, so I will not even take the time to consider a refutation.
Clearly, it seems, you have taken it way too personally and should walk away from the game for a few hours.
Some activities in nature are great to help release oneself from our stressful lives.