Ask HN: If Security by Obfuscation is bad, why does Google Drive do it?

When you share an item with someone, Google creates a unique link for that resource and person. We always hear that security by obfuscation is bad - but can it really be that bad given that Google Drive does it? I just shared a folder with someone and in the email it says this: This email grants access to this item. Only forward it to people you trust.