It seems to me there is no difference in kind between an email arguing for or examining an important decision or idea, and an "essay" on an important decision o

It seems to me there is no difference in kind between an email arguing for or examining an important decision or idea, and an "essay" on an important decision or idea. Why are there people who make a living as, say, newspaper opinion columnists or magazine staff writers? Or hell, why aren't we all rich substackers given that writing a substack is literally email?