They are persons for historical reason, it's just like that table at the center of your DB with a terrible name - changing it now would be immensely expensive due to all the dependencies so we just accept the table is poorly named.

In the US a certain set of rights are given to "persons" that should really be given to "legal entities", I've never had a conclusive answer as to why but I'm just going to guess it was a lack of foresight. Over time there have been judicial rulings, national laws, local laws, and other fun stuff that have slowly corrected or clarified the definition of a legal "person" that should apply to all things labeled "persons". Some of these you may or may not agree with (maybe only "natural persons" should be able to participate in the political system and such) but the general approach of clarifying the term even if the term isn't perfect is a pretty good approach.