I think that's kind of narrow-minded actually. There may not be actual surrender options in other sports, but there are plenty of times where the game is essentially just let to run to completion without any attempts to keep playing competitively. For example you'll see "keep away" played in soccer to run down the time instead of running up the score or you'll see the game slow down and just become recreational after sending offs or injuries. In football you'll see games that are blow outs where the winning team sends in their second or third string players to let them get game time instead of keeping the first string out to play. You'll see games where both teams just switch to running every down and not using time outs to run out the clock faster and end the game. Then there is taking a knee in football which is essentially saying "let's hurry up and end the game because it's already over".
For League, I feel like it can be similar. If the team just got aced at the inhibitor and the respawn timers are up to the 45 second or higher set, then it's often times obvious that the game is over. So instead of wasting 20-30 seconds of the other team just standing there clearing a minion wave and taking down the nexus turrets and nexus, they surrender to just move onto the next game. That doesn't seem unprofessional to me at all. I will say that there are times when that isn't the case. I think I've seen maybe two games in between season 3 and season 4 so far where a team surrendered after a bad teamfight or a baron steal, and in that case I do think it is inappropriate to surrender, because you are cheating the spectators out of watching the rest of the game play out and you're cheating the other team out of a proper victory and it injures the competitive integrity of that match.
By the way, in case you didn't know there actually are penalties for quitting in an inappropriate situation in professional League. For example Millennium in the EU LCS had a game where they lost a ban because while the enemy team was taking the Nexus in the previous game, Aranae (rage)quit out of the game before it was over and threw down his headset. There are punishments for inappropriate and unprofessional behavior, but I think surrendering to save 15 seconds isn't unprofessional.