Neither do Google+, Pinterest or any of the other social networks.
Put simply – Despite repeated claims by people in various photography forums these companies do not in fact own your photographs just because you uploaded them – they just licensed it for use on their systems.
The more detailed explanation is – These are multi-national companies and while they may appear to be one big company they are actually a group of separate legal entities (Facebook US, Facebook Canada, Facebook India, Facebook Ireland etc) each running different parts of the operation. When you join one of these networks your contract of service will be with one of these companies. In order for your pictures etc to be shown to your friends in France, Aunt in America and cousins in Australia, they need to transfer your content between the different companies that make up Facebook/Pinterest etc., which they can’t legally do unless users grant them the right to do so. That is the purpose of their terms of service.
So, while the license allows them to move your content around their network in whatever form is necessary (for it to be displayed on various different hardware platforms) the companies use of your content is limited to their system. They can only do the things stated in the license within the boundary of their own system. They can not sell your content to someone else or publish it in a newspaper etc etc.
Specific quote from Facebook’s legal agreement page at https://www.facebook.com/legal/terms?
Sharing Your Content and Information
You own all of the content and information you post on Facebook, and you can control how it is shared through your privacy and application settings.
There it is, plain and simple in black and white.