Because there is no difference between winning and losing inside a video game. Unlike real life, surrendering means saving your life. In video games, surrendering does not cost you anything. You will continue to press Q, W, E, R, D, F, and 1-7, again and again. The only difference is a stupid "Victory" or "Defeat" sign that appears on your stupid profile. If you deserve a higher rank you will get there, one or two extra games will NOT help you.
Even if you are losing, you should enjoy losing because it is a challenge, it will help improve you, and force you to play better or continue to whine and complain like 90% of the pathetic defeatist losers in this community.
90% of this community does not know how to play from behind, cannot handle a LITTLE bit of pressure or stress, and give up when shit gets tough (in a video game). It tells a lot about this community, it is filled with losers.
If you CANNOT handle League of Legends, you probably cannot handle real life, if a silly little game can make you give up or surrender, wait till you lose your eye, a limb, a wife, your money, your family, or your job. That is the bottom line. Surrendering pathetic losers are losers in real life. End of Story.
Never surrendered since 2009 and never will. So get use to it.