The list of internal followers on a Zendesk ticket is a core piece of information that is for some reason being left out of the sync process to BigQuery. Quoting a support ticket I opened:
I've had a look at our schema, and it doesn't look like we are syncing this data.
Zendesk's API reference shows this is being included in responses coming from the tickets endpoint but we are not making use of this data at the moment.
Can you prioritize adding support for this? It seems that this data is right there in the API call you're making to tickets, but your backend is just ignoring it.