What causes accents?

Sharon, at work, has THE HEAVIEST Chicago/Midwest accent I've ever heard.
One thing you can't tell by writing is an accent, but I'll try to spell out how Sharon says certain words:
Patsy..."Payatsee"
MassMutual..."MayassMutual"
It's different than a Minnesota accent, because it's not spoken as quickly and not as cutely put together as the Minnesota "park the car" accent. Sharon's is kind of wild and spoken slowly and on purpose so that we can understand each word she says. Maybe a little bit of New York thrown into the Chicago accent.

On the other hand there's a woman who just started here from Wisconsin who doesn't speak much differently than I do. Is it up to each person individually how much they take on the accent??

Lisa, the woman in the cubicle beside mine, is an obvious east coaster...she sounds like the Italians (Sicilians) in the Godfather. She sounds directly from New York. I love listening to her talk, especially if she's going on and on about something or someone and throws a few curse words in. :) Like Rosie O'Donnell with a whinier voice.

Speaking of whiny voices...I've noticed that canadian woman have lower fuller voices than many mid-western people. I don't know what it is...maybe it's that a lot the midwestern girls I've been around have been surrounded by girls who are "blonde" and stupid and they like to be bubbly and prissy? I know that's totally dissing midwestern girls, but I've noticed that the words "like" and "you know" and "not gonna lie" come out of their mouths WAY too much. I don't mean to offend any girls, but I do try to stay away from a high whiny voice and especially filling my language with the words "like" and "you know."

Added later: Okay, this is not to say that ALL midwestern girls are whiny and stupid! And I know there are stupid whiny canadian girls, too! my roommates from the midwest are an amazing exeption to this "like, you know" rule. Lynae you're very intelligent and don't have a high voice. Your voice is very womanly and voluptuous and you DEFINITELY do not fit my typical stereotype. I am serious, and I'm sorry if I've offended you! I'm proud to be your roommate and hope your awesome personality and good qualities will rub off on me!