Aliya Summary: After concluding the subject of tzara’at, the Torah discusses the ritual impurity of a man who issues a sickly and unnatural seminal discharge, as well as the method by which this person attains purity when the condition passes.
Rashi points out that the discharge contaminates only if it’s on a portion of the body, but if the entire body is discharging, the person is still pure. Logic would dictate otherwise, unless you view it as an indicator of specific internal issues that need to be addressed, and having an entire body secrete anything is not operable or helpful. You can’t tell someone “everything is wrong with you” and expect them to be able to do anything about it. Being “impure” means that the person needs to fix something about their character traits, and that just isn’t possible with a full-body discharge (a separate question would be why a full-body discharge would ever happen, if it’s inoperable).