Why is it that religious iconography was and can be soo effective?
Are people really that stupid?
Maybe.
Except for the people that promoted it, of course.
They were better, smarter more evolved than the rest.
Lots of reasons. Most of which we only started to understand in the hay days of Madison avenue. There are certain looks, certain ways to color and arrange things, certain images, that trigger certain human instincts. Properly deploying those idea can make people respect you, obey you, and buy crap they don’t need.
I wouldn’t say they were better, smarter or more evolved. They just paid attention to stuff that most people didn’t then, and still don’t. They noticed the fact that most empires use the eagle as a chief symbol. They noticed the prevalence of red. The block fonts. The first guys probably stumbled on this stuff by accident, maybe a bit of watching how crowds react. The rest just read their Roman history. The funny part is even if you know about this stuff it doesn’t make you immune, just means you know how you’re being manipulated.