Missing Project and Namespace IDs in structured events

From a Slack thread:

I'm mainly curious why dim_namespace_id and dim_project_id are null in so many self-managed events 🤔 I'm querying the prod.common_mart.mart_behavior_structured_event table

I was looking into this a bit more with this event (users_creating_work_items) and noticed that most of the occurrences of null Project/Namespace columns are related to events where the plan_name is default or unknown on self-managed instances. I'm also curious why we can't determine what the plan name is 🤷 🤔

Queries I was playing around with:

SELECT 
  *
FROM prod.common_mart.mart_behavior_structured_event
  WHERE event_action = 'users_creating_work_items'
  AND app_id != 'gitlab-staging'
  AND plan_name = 'Unknown'
ORDER BY behavior_at
LIMIT 1000

SELECT 
  plan_name,
  COUNT(*),
FROM prod.common_mart.mart_behavior_structured_event
  WHERE event_action = 'users_creating_work_items'
  AND app_id != 'gitlab-staging'
GROUP BY 1