And why is it spammed so much in twitch chat and even during blast premier final?
Because he has a lot of delusional fanboys. He is most likely the most famous Valorant player and there's still bunch of people who thinks he is undisputed number 1 player. Popular among people who have no idea what they're talking about. In a way he is "player for normies". And BatChest in this context reflects those people and usually "I hecking love...." is used with that emote.