Facebook I can explain, since the company and the main product are identical. But what about the others? Why do we need tags for companies instead of their product?
I'd argue that these should be burninated:
Does it describe the contents of the questions to which it is applied? Is it unambiguous?
I would say No to both of these. It's unclear whether these apply to the company, or any product they offer. Most questions e.g. for microsoft are about a specific product they offer (e.g. Windows, Office, etc.), not the company themselves.
Is the concept described even on-topic for the site?
Does the tag add any meaningful information to the post?
Does it mean the same thing in all common contexts?
Yes. Microsoft is a company. That much is a given.