At a mass scale, the users on the network are not sophisticated or trained, and end up having very common failures that result in a move to a trusted central authority.
Your account got taken over? Need to reverse transactions? Need recourse if someone defrauded you? Don’t want to check each factoid you read? Need to ensure that users are not spreading actual terror content?
Bad actors alone, are a sufficient force that generates social pressure that drives centralization through regulation.
But thats an easy example, the other force is the unsophistication of the average person - as a result they gravitate towards tools that simplify their lives, and do a lot of the work they are not interested in doing.
When network effects come into play, this creates a pressure where firms with more resources buy smaller players and consolidate, once again creating a small network.
People don’t want to deal with the over head of creating new accounts for example, or the overhead of moving their content from X service to Y.