"Try hard" is an insult that originally meant people who put on an image of a certain style and end up looking fake or contrived. It didn't make much sense in that context anyway.
In this case though, it seems to have been taken up by people who can't handle losing and therefore want to accuse others of being "try hards" i.e. putting in too much effort. But usually, of course, it means that they're the ones trying real hard and still losing, can't deal with it and so yell insults.
Do your best and ignore what people say, trying to win is what most people are doing in a game.
Next, they'll make "winner" an insult just because of how hard it is on people who care too much if they lose. "Damn you, you, you... WINNER!" I can totally see "winner" as becoming a word that means "selfish" someday.