it's a glados quote

 guys “the cake is a lie” isn’t even a quote said by glados…….. its the plot twist of the game… that’s why its a repeated thing people say because it’s like a cautionary warning scribbled on the walls by ratman

and it isn’t supposed to be funny like i guess the absurdity of it is funny but glados doesn’t really talk throughout the game, and when she does its at the end because she’s trying to demoralize chell

but dont get indignant bc people quote the cake is a lie and not the other funny shit she says in portal 2 bc when people were saying the cake is a lie it didn’t even exist yet