Why does vomiting phlegm (Balgham) NOT break Wudu in the Hanafi school, even if the amount is excessive?

Wudu: Ten Things That Do Not Invalidate It

• Because phlegm originates from the stomach.
• Because phlegm is legally classified as pure (not a physical filth/Najasah).
• Only if the person was fasting.
• Because vomiting is always recommended.