MSFT and FB want to maintain and increase access to the 1.35 Billion people of China. Not ironic at all, those companies need to be in China even if treated poorly.
Facebook is completely blocked in China, as far as I'm aware. In fact, it's not just blocked, a DNS lookup of facebook.com is returns a bogus IP address. I can't see why Facebook would think that they have any hope of getting unblocked, unless they are willing to let China's censors do their thing with Facebook posts.
Except Google. But standing on principle is pricey.