Commercial overload and noise. Attention is split into bigger and bigger share among the top players and is constantly gamed.

Disinformation and government ability to censor in one swoop compared to a private group made of few or many people you know or have similar interest with.

Rising nationalism? Politicians are catching up and government is pushing for alternatives to US tech giants and ability for other countries to influence their people.

Generational change?

Long term - when universal income is a thing or there is more time allocated for your hobbies, people will have time to invest in their particular interest groups and such. Currently, many don't have much time to do it so they rely on centralized sources for their stuff which is filled with noise and too many different people they don't know.