If my local government or some local business was limited to using one specific newspaper, this would indeed be a problem.
And in reverse, having a concentration of readers (users) on one platform, means that whoever controls that newspaper (platform) gets to be kingmaker for the government and the businesses.
Free speech as a constitutional requirement binding on a government to allow it is great; that government then using one specific private corporation that can use its own status as a non-government actor to have free speech rights rather than free speech responsibilities, means it is a de facto loss of free speech for everyone else.
There is no constitutional entitlement to receive government information through one's preferred newspaper, website, or social network.
> it is a de facto loss of free speech for everyone else.
You seem to be confused about what 1A is and what it guarantees. It is a restriction on government action against your speech, not a general requirement that everyone have equal access to every privately owned communications channel.
Re:
> There is no constitutional entitlement to receive government information through one's preferred newspaper, website, or social network.
and
> You seem to be confused about what 1A is and what it guarantees.
I am arguing that there should be, and why; I am not arguing what is.
Also I was careful not to use the words "first amendment"; this is because this argument, and this problem, applies more generally than just the USA.
OP's point is that creating a favored restricted platform natrually allows for restricting of free speech because of a private "compnay policy". ("allows for" is doing heavy lifting here btw)
Should a government choose to communicate essential facts only through a restricted medium it is obviously no longer serving the larger public interest and thus no longer a government of "a people for a people".
Musk and fellow techoligarchs can have their private platforms.
Free peoples' governments and responsible social organizations must treat them as 'for profit entertainment channels' and not give them any legitimacy in the political space.