If it were otherwise, then what's to keep from having a company city, or company state? Sell off Seattle to Bill Gates, and make it his fiefdom.
Sure it does. Entering someone's land when they've told you to stay out is known as "trespassing".
> If it were otherwise, then what's to keep from having a company city, or company state?
Assuming the land is legitimately homesteaded and purchased? Nothing. And there's nothing wrong with that.
https://en.wikipedia.org/wiki/Freedom_to_roam
That points out that "Ancient traces provide evidence of the freedom to roam in many European countries, suggesting such a freedom was once a common norm."
It's also been noted that the freedom to roam is strongest in those areas which didn't have feudalism and serfdom.
Just like feudalism and serfdom, company towns have a history of being controlling and exploitative .. and un-democratic. That's what's wrong with them.
However, the issue in this case is not restrictions imposed by property owners on the use of their own property, but rather restrictions imposed by the federal government, which is bound by the limitations on government power written into the Constitution.