But I don't understand the connection.

The core of the issue is the proverbial "worse is better"

All the walled garden on the web are optimising one particular feature - engagement - leaving behind many others that are equally important if not more, like user's freedom or privacy.

It's no wonder that investing so much money in getting users to subscribe and use the platform results in an increase of time spent by the users on the platform.

It is orthogonal to the problem highlighted in the original post.

The net effect is so strong that any other platform that tries to enter the market either has to waste a lot of money (if they have them) or use the same techniques that are already in place to sustain their businness

The choice is on the users, but for the majority of them it's not worth it until it's too late.