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Facebook could do something similar. They have the money and team to develop it. But no one is asking them to do it because their millions of members are happy to be able to do whatever they do there, without getting anything back from Facebook other than the service of the platform. Everyone is already on there so Facebook doesn't need to do anything to attract new users.

But if Steemit gets big, and people start leaving Facebook, they might make changes. But it might be too late. Similar to what happened with MySpace. Once everyone decides to move on, the old platform collapses. Well that's one possibility anyway! I really don't know what will happen but I'll be here to see whatever does happen!

I think FB is studying this case. Of course if FB will decide - FB to make a "copy" of steem in a single day . He/she doing quality posts - > gets likes - > and then he/she become a marketplace. Thats all

if fb would make more money that why, they would do it already

It really depends on what you mean by the same thing.

If you mean with paying out for interactions, where would the money come from? Facebook may decide to create their own blockchain currency, but that would mean giving up a measure of control over their network.

Also, remember that steem uses a decentralized architecture, which means that nobody has control over it. Something that Facebook just could not deal with.