The Honour system started out with such an option. I don't exactly know what drove riots decision but I have an idea from some stuff I read.
Stuff I believe: I doubt it helps reducing toxic bragging. These people who don't know how a "shake-hands" works will spouting stupid braggy stuff.
Stuff I know: The Opponent honour was frequently misused to make fun of enemies by honouring the worst player of the opposing team. It was not used to recognize and reward honourable play, it was used to show who was an integral part of losing the game for the other side.
Either bad players or feeders were honour after all they won you your game. I don't know how often that happend. I have seen very much respect for enemies at this time. Basically as it is today. Some say GG and some stay around to talk about the game and close calls builds and how you had no chance anyway due to counter play etc.. And some write "GGEZ" and go in in post game to show of how great they are and how bad you are.
I don't know the ratio or if it changed over years, but it seems like this abuse of the honour was frequent enough for Riot to deem it "toxic" and tilting for to many players.
I aswell would like to honour honourable players on the opposing team. I get Riots rational but I am old enough to just not read or take to personal when some kid thinks he/she is the pinnacle of human evolution.
