I think it's more about convenience and bypassing filters - developers are already logged in to github, already have access to create repos and publish code, firewalls will allow it. Even fancy HIDS systems will think the git push is rather normal.

If they have a clue, the attacker still will not download that without using a botnet tunnel or Tor at a minimum.

Note though that these credentials aren't even encrypted using some lightweight ECC to prevent others from capturing them, they're posted in cleartext. Embarassment might be part of the point.