In theory the reason for this is that Facebook is "stickier" than Google or Amazon. If Google search isn't working for you, you can switch to something else in a heartbeat. If Facebook isn't working for you, you have to get all your friends to switch to something else before you can.
The problem is this is also going to be Facebook's downfall at some indeterminate future date. Because if some other social network ever becomes more popular than Facebook, Facebook is over.
I'm relatively tech savvy, but I'm not sure my significant other would know where to go if Google was down. DDG or even Bing are not top of mind. What else is there?
bing is actually pretty good. sometimes google's selection bias to what it knows about me prevents me from getting to the results I want so i either search in incognito mode or search in bing.
It was a social network; just an inferior one to Facebook. They lost to Facebook because Facebook was a more pleasant site for social networking, which made it more popular.
If you were in Germany, you may not have seen this, because MySpace didn't enter Germany until 2006 or 2007. At that point, Facebook was already starting to beat them with new users. By 2008, the established user base of MySpace was fleeing in droves to Facebook. The network effects that would have created social pressure to stay actually caused it to collapse even faster.
There is nothing that would prevent this exact thing from happening to Facebook. If a better site were to come along (or if Facebook were to become vastly less competitive than they are now), the social pressure could actually cause them to collapse just as fast as MySpace did.
The problem is this is also going to be Facebook's downfall at some indeterminate future date. Because if some other social network ever becomes more popular than Facebook, Facebook is over.