Perhaps it is because whoever came up with the specification for "browser cookies" never intended them to not expire, and thus you are trying to subvert the fea

Perhaps it is because whoever came up with the specification for "browser cookies" never intended them to not expire, and thus you are trying to subvert the feature to do something it wasn't meant to. The Jurassic Park quote comes to mind: "Your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should."