1. start interesting conversations.
2. provide feedback for the quiz maker to show that I took and appreciated the quiz. As a prolific quiz author myself, this is important to me.
3. offer constructive criticism. Something else I appreciate as a quiz author.
Reasons I NEVER comment:
1. to brag or make myself feel good, smart, etc.
2. to complain about the quiz, except in very rare instances and those are usually user-created quizzes that suffer from bias or something along those lines. I don't recall ever seeing a front-page quiz like that.
3. to take away from anybody's fun.
4. because I imagine I am competing against anyone here for any reason
I will occasionally comment to correct grammar, but that is exceedingly rare, as well.
So, I maintain, for those who know what they're talking about...
But I bet a big part of the reason both LA and Miami show up on the list is that if they polled anyone in South or Central America it's very likely that they have a friend or family member residing in one or both cities.
But I guess foreigners do have a glamorous perception of it. When I was teaching in Asia I was constantly getting asked if I knew people like Arnold Schwarzenegger and J.Lo.