Because it is a private enterprise that you signed up for. You don't have a right to Twitter. You don't have a right to Facebook. If you don't like it, leave. The entitlement is massive here. These sites are poison in so many ways. Stop feeding the beast.
Regulation over communication channels is not only common through the ages, but expected and needed. There may not be literal landlines to worry about in the modern age, but the general idea of communication being an important medium that shouldn't be squandered by competition remains.
I prefer everyone to simply leave Twitter and to let it crash and burn, but I see the arguments to have stronger regulations on channels central enough for governmental entities to be using it as a communication hub.
Multiple government agencies have a gap in capability. Larger government body chooses to leverage a popular (private) company Z solution over trying to develop an internal system. This is often because it's already been done in smaller jurisdictions. Z becomes head of agency/regulatory capture cartel. Z abuses the position to curtail the government actions/enable further corruption/abuse.
But I do have the right to the public information posted by people who intend it to be public information.
They're not posting 'on X', they're posting to the public and the only reason they do it on X is because there are no alternatives due to the network effect intrinsic for such services.
The 'network effect' part needs to be defined and taken into account by regulators and then regulate the companies such that they make the information available to the public if the poster intends so.