Actually they are. Look up the definition of a corporation.
This was not some accident of the law: this was deliberately designed hundreds of years ago and is well understood outside of internet comment sections.
A corporation is a unique legal entity that has a limited subset of the rights of a person, but is not considered the same as a person as a blanket statement.
Specifically, a corporation is considered a "person" for the purposes of being able to enter into contracts, being able to sue and be sued, and similar.