We don't live in a libertarian utopia where private property is not regulated. If you're a store-owner, for example, there are some things you simply cannot do or must allow. In California, for example, a private space, like a mall, has to allow constitutionally protected speech[1].
You can regulate platforms to allow for, say, free speech rights.
[1] https://en.wikipedia.org/wiki/Pruneyard_Shopping_Center_v._R...
"under the California Constitution, individuals may peacefully exercise their right to free speech in parts of private shopping centers regularly held open to the public, subject to reasonable regulations adopted by the shopping centers"
