So they should be punished for having a bad game? 10 deaths in 15 minutes isn't basically GG, believe it or not, although it certainly does make it much harder. If the team keeps playing defensively, by the time everyone hits the late game it no longer matters who had an early advantage because everyone is at the same point. Granted, it then makes it harder to survive until the late game but that's just the price paid. On the other foot, a teammate going 0-10 has stopped giving out meaningful amounts of gold and xp. They're basically no better than a large minion. So it could actually be a positive thing at that point, because instead of trying to push their advantage elsewhere they're wasting their time on weak target while allowing other teammates to get strong enough to make up for it.
And don't forget, if you have a teammate who's going 0-10 in 15 minutes, it's also because they were clearly having an issue being alone but no one on your team went to help. Your jungler, your ADC, your mage, your support, your tank, whoever else, everyone else on the team is just as at fault because it's a team game and while you all recognized that a player on your team was having an issue no one went to help. You might not always be able to, but at the point I have a teammate who's just hemhorraging gold and xp like that I'll at least try and give them a ward or two along river. I'll gank them extra. I'll roam from my lane to go and try to give them breathing room to farm.
No one ever wants to admit it but everyone is at fault if a teammate is getting shitstomped provided that they aren't just trolling. And, once again, I repeat that there are several options for reporting someone for that sort of behavior.