Spammers are using them to advertise gold selling, not only that is illegal but also whenever a long message shows up it causes a graphical lag spike in the game. When they spam a lot you can even have issues moving around / turning your character to cast skills.
Please give us an option to disable megaphones messages for good or remove them from the game completely.
EDIT: Please don’t come here just to post “oh but you can block them”. Those spammers make new characters everytime they get kicked/banned from the game and blocking them each time they make a new character gets annoying.