Why have we let X (et al) have total control over the content posted by the users ?

Why do the users agree to the limits imposed by them and let the platform decide who gets to see the content they posted ?

Because they're offering the infrastructure. The tech for such a network is now within reach of many, but these apps are heavily dominated by network effects and that makes it impossible for competing apps to take hold.

This is negative for society.

Firefighters who deal with forest fires, police, governments, rescue services (here in Spain) are all posting their updates on X - because, like the users, they have no choice, because no alternative exists.

People who don't have an account are not getting vital information because the company decided to restrict access to the entire network.

This needs to be regulated somehow. At least for public services and major news outlets - as a tax for the network effect these apps benefit from.