Why do people keep baiting me into a new game!

This is happening so much lately. I play a Ranked game with 4 people I don't know. One person stands out, we play very good, we win, and after the game I ask them to play again. Because we were shining on that game. And then the game starts, and they start to go play completely nutcrackers? Like it's another person. Feeding, no warding, trolling, going afk, jumping into a group fight on his own everything. So at Game 1 they are amazing and then game 2 they are completely insane!? Sometimes even the same role... Are people having fun doing this? Baiting people into playing with them again and then totally screwing up the game? Sometimes accompanied by the chat messages LOLZ and WOOPSIE. It really drives me insane
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