I see so many posts and comments about why a surrender option is needed, I have to react.
I'll start with something simple to understand : MATHS :-)
In a game, you can either lose or win. Wow, great news.
What happens if you don't surrender ? Supposing the matchmaking is accurate, you have 50% chance to win, 50% to lose. That can vary, but even in a 40/60 case, the game should be playable.
What do you have to consider to accept a surrender vote ? Supposing you are WAY behind, your team is trolling, you don't even want to play anymore, etc. This can happen to anyone. Actually, this eventually will happen to everyone. Well. You had 50% chance to win before the game starts. Is that chance 0% now ? If it is, then surrender. But is it ? How can you be sure ? Even the greatest player in the world can disconnect. Have a power cut. Collapse and die on his keyboard. I don't know, but still, when you think there is no chance, it's not 0%, it might be one out of a billion, but there's still hope. There are so many parameters to take into consideration that I don't think anyone would actually be able to tell if a team will be losing or winning with 100% accuracy.
What happens if you surrender ? This actually drops the last percentage of chance you had to 0%. Ok to be faire, it might have been 10%, or 5%, but even if you had 90% chance to win, this drops to 0%. So now, with a surrender button, you have two ways to lose : losing, and voting "please let me lose". And only one way to win. Not fair.
Why a surrender option is not a good idea ? With the surrender option available, people will consider this option every game. They'll stop fighting as soon as they see a hint of defeat. "First blood ? Our chance is now 0%, let's surrender !"
Why would it be necessary ? No, really, I've been trying really hard. But I can't see a reason. Have you ever seen, in any sports, a team surrender ? When you are [insert small village name here] and you play FC Barcelona, you are ready to get your 20/0, but you play. Do you know why ? Because there is no surrender button in football games !
tl;dr: WE SHALL NOT SURRENDER, SURRENDER IS FOR COWARDS