[MattDemers]

You end up having a cyclical problem, though:

No one uses it because no one posts > No one posts because they don't expect interaction > No one expects interaction because no one uses it

And then brands or influencers don't join because there's no potential to make money.

Part of the history of these big incumbents is that people were discovering a more user-friendly way to use the web through them; Facebook, Twitter, Instagram, YouTube all were "Hey, we can now do something we could do before, much easier, in a more accessible way that I can show to my normie friends/my parents."

Alternatives that DO come up, like 500px or Vimeo, end up needing to become more for enthusiasts (people who care about fidelity, rather than novelty), turning away normies in the process. That's fine for them, as long as their goal isn't to "be an alternative YouTube/Flickr."