The constitution applies to the government. It establishes the government and defines -- and therefor limits -- what the government is allowed to do.
Corporations are considered "legal persons" for the purpose of applying the law to them in a convenient and organized way, but in real life, corporations are just organizational models employed by human beings for the purpose of coordinating their activities.
The restrictions applicable to what the government is allowed to do to "people" as defined in the constitution apply regardless of what organizational models those people are using to coordinate their activities. Ultimately, everything in society reduces to people, and the government is not entitled to use reified abstractions to escape the constraints on its authority.
Corporations are considered "legal persons" for the purpose of applying the law to them in a convenient and organized way, but in real life, corporations are just organizational models employed by human beings for the purpose of coordinating their activities.
The restrictions applicable to what the government is allowed to do to "people" as defined in the constitution apply regardless of what organizational models those people are using to coordinate their activities. Ultimately, everything in society reduces to people, and the government is not entitled to use reified abstractions to escape the constraints on its authority.