The reason they are called corporations is language and vocabulary. The word is like body, as in the body politic. The etymology of corporation is Latin compare

The reason they are called corporations is language and vocabulary. The word is like body, as in the body politic. The etymology of corporation is Latin compare "combine in one body" or "persons united in a body for some purpose". That is why we have the word. Everything you added is modern and irrelevant to the question of why we use this word.