Question: Why are eclipses of the James Webb by the Earth or Moon not permitted during the mission?

In https://ntrs.nasa.gov/api/citations/20150017756/downloads/20150017756.pdf. it is stated

Shadows, or eclipses of the spacecraft by either the Earth or the Moon, are not permitted at all during the mission… these constraints conspire to limit the maneuverability of the spacecraft and couple the orbital dynamics to the rhythms of the Earth, Moon, and Sun.

How come? The cold “science” side of the spacecraft is already eclipsed by the sunshield. Communications interruption should not be an issue since communications are intermittent anyway.

The Earth's umbra extends 1.4Mkm https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra and the JWT is 1.5Mkm from Earth, so the telescope would never be completely eclipsed in the worst case. Since it is in a 0.8Mkm halo orbit with a period of 6 months, it would take about 18 hours to traverse one Earth diameter or 36 hours to pass through the penumbra.