Meth vs. Coke: What leads to what?

I Google and what not….but what I always come up with is that meth use leads to cocaine use, not the other way around. Why is that? I’m confused here: Wouldn’t a person who has severe addiction to cocaine be using meth as well? Does coke abuse lead to meth use? Oh also, would coke addicts also be using heroin as well if available? I’m doing a paper for school….that’s why I ask so mnay question re illicit drugs and their use/abuse. Thanks a ton folks!
Okay..all comments considered. However, let me make a hypothetical scenario: I’ve been doing coke for many years, in between those years I’ve heard what a bigger “rush” and the longer lasting effects of meth can produce, so I began using meth in lieu of cocaine. *Sidebar: I never have used drugs other than have messed with pot in high school waaaay back in the day. My point here basically is would a coke addict ALSO be using meth in as well?