I guess the difference is relativity. Esports popularized in Korea, specifically PC esports, where good manners is absolutely essential. They actually disqualify you in the GSL, a starcraft 2 tournament, for typing anything other than "gg" because anything else can be disrespectful. So seeing how that was the standard for so long, you can see why this is considered bad.
Koreans are polite but not that polite. Firebathero, a Brood War player who created his entire image around bad manners. People loved this dude even though he had flagrantly disrespectful ceremonies. In one instance, he won a game and started humping the air furiously towards the direction of the crowd.
"You are my rice" is a popular phrase in Korean, which basically translates to "you are my bitch". The implication is that I am so superior to you that you don't even qualify to be my prey. I don't have to do any work to dominate you. No chasing, no hunting, no effort required of any kind -- I can just eat you like an inert serving of rice.
He threw a bowl of rice at a player after winning a Proleague match. The implication was pretty clear.
So Koreans actually love bad boys. They aren't just a bunch of robots obsessed with decorum and professionalism. There are lines that can be crossed but that's a whole other discussion. I work in esports and I've translated for Korean StarCraft players in the past. The reason why they tend to be so reserved in western tournaments is because they're in an unfamiliar place (most of these kids have never left Korea until esports) and they have no idea what's culturally acceptable or not, so they err on caution. Years ago when I told Boxer that western fans actually like seeing overt displays of emotion and even bragging, he was really shocked. That wasn't his image of western sports at all.
Also, GOMtv's GG rule isn't about disrespect, it's basically an extension of KESPA's ruling. There's too many headaches to deal with by allowing chat. Bad manners is part of that, yes, but the biggest culprit was ambiguous surrenders,