It's supposed to be identifying information here. Usually, you can just send copies of those documents, which means that if you're looking to impersonate someone, you can easily produce fakes. And since everyone and their grandmother asks for these, people don't bat an eye and send them.

The coup de grace of security in France is signatures, though. Now, since you can't produce a physical signature over the internet, they'll ask for your phone number and send you a text with a code. Once you've entered it on their web form, you've proved undoubtedly you are who you say you are.