Matrix and the power of decentralized federated social networks will allow this soon.

Yes it will! https://github.com/KombuchaPrivacy/circles-ios

Does Matrix support full extensibility of data structures or are you tied to some minimal model?

full extensibility

It's also that they have reason not to change up things. They have created vibrant monetisation mechanisms & fine tuned those mechanisms.

Innovating means new patterns of interactions & ideas. This also means new forms of monetisation that might be required.

As an example all the previous FB & instagram ads became obsolete or useless once they introduced stories. Now, have to create better ad formats and subsequently take few quarters to fine tune the experience and pricing.

How do you define success for these experiments? Social media already is optimizing for engagement, probably the average hn commenter doesn't like those results though.

Agreed. Wondering why social media companies aren’t trying to make the platforms less engaging is like wondering why drug dealers aren’t making a less addictive opiate.

obviously every platform wants engagement, they want you to use their product over others! but I think that's only part of how you define success, which obviously will differ platform to platform

like I think something like "sustained high quality discussion" is good goal other spaces like HackerNews aim for