Someone, probably: People who don't know how their services work are doomed to spend lots of money on them.

From the GCS pricing page:

  Network egress within Google Cloud applies when you move or copy data from one bucket in Cloud Storage to another or when another Google Cloud service accesses data in your bucket.

  Within the same location (for example, US-EAST1 to US-EAST1 or EU to EU) -- Free

From the original tweet (not the linked reply):

  For reference most of the fees are from transferring from NA to EU and ACAP

It's costing them assloads of money because they're moving data between regions. AWS works the same way. Azure is probably also the same but their pricing page is incomprehensible so who knows.

Lesson: if you're going to use data in a given location, you need to host data in the same location.