It goes back to 1886 [1]. Ditching corporate personhood just makes the law convoluted for no gain. (Oh, you forgot to say corporations in your murder or fraud statute? Oh no!)
It gives rights, not obligations, which makes Citizens United so abhorrent. It's a dark money vehicle, and worse - foreign dark money. Just on the face of it its ridiculous, but alas, laws are made by the ultra rich.
A corporation has the right to "speech" but if crimes are committed, rest assured it will not go to jail, and neither will its executives, protected by layers of legal indirection of this "person corporation".
This gave us the Citizens United v. Federal Election Commission, 558 U.S. 310, i case on their right to speech or place funds.