The rights of assembly and petition applies to private property as people don't have the right to intrude on anyone's private holding even if it is to express political views.
Explanation
Everyone has the rights to freedom. People can express their opinion and views without fear of judgement.
Besides sharing an opinion, people can assemble as per the First Amendment in public areas.
But private properties are places owned by individuals with their own interest. And everyone prefers to have their own privacy not to be disturbed.
