Psychology of password generation

As we all know, password generation can be a tricky task. It takes a fair amount of training to be able to generate actually secure and at the same time memorable passwords. Without such training, password generation will depend entirely on a few, predictable principles of human psychology -- people will tend to choose "password", or stuff that is personally meaningful to them (e.g. "football" if they like American or soccer football), or stuff from mainstream pop culture (e.g. "superman"), or stuff related to a website's theme (e.g. "pussy" or "696969" on a porn site, "elohell" or "doublelift" on League of Legends). This topic came to my mind after reading a couple of articles on the topic of psychology of random number generation, like this one that addresses what does 17 have that it looks like the "most random" number to most people.

However, while studying the 10,000 Top Passwords, I couldn't help but notice some passwords whose popularity seems a bit unexplainable. Why so many people tend to choose "dragon" and "monkey"? What do dragons and monkeys have that so many people think of them when asked to generate a secret password? Why is "michael", of all people names, the one most commonly used as a password? Why seemingly random words like "sunshine" or "pepper" are so commonly picked?