Ford was never considered a monopoly. GM and Chrysler have been around since the early days. And even in the Model T days there were plenty of other cars. Also, Ford never went bankrupt, you might be thinking of Chrysler or GM, both of which filed for bankruptcy in 2009, although neither ceased operations (so not "bankrupt" in the colloquial sense).

Facebook, on the other hand, what other network can I use? Twitter isn't really the same thing. Most people outside of China don't have WeChat (and why would I voluntarily give anything to the Chinese government). Same with LINE (Korea, Taiwan) and VK (Facebook for Russia). Instagram, which really isn't the same as Facebook is owned by Facebook, as is WhatsApp. The only competitor is Google+, and is that even still going? Is it really a competing social media network if no one I know is on it?