Why did the CDC change the definition of "Vaccine"?

We obtained CDC emails via FOIA for the answer.

CDC emails:
Our vaccine definition is "problematic and people are using it to claim the COVID-19 vaccine is not a vaccine based on our own definition"https://t.co/gCW7Flv2xA

— Techno Fog (@Techno_Fog) November 2, 2021