@rockyboy1998Because they like to grief new players, because they do it for content creation, because they have friends they want to play with that have not enough skills to make it into higher ranked lobbies. Maybe also because they help boost others accounts. Some may boost it to pred/masters and then sell it (someone may buy those accounts for bragging rights?).
Because once they plateau they do not want to put in more efforts to move forward?
Who knows for sure.