and if I'am not mistaken it started at first as a coffee substitute and some people got a taste for it and started adding it to their coffee when the supply stopped being too short.
You are not far off. From what I remember, chicory is native to Europe, Africa and maybe Asia. I don't know how it came to the U.S. It's been used as either a coffee substitute or to extend coffee since the 1700s. In the South, chicory became a substitute for coffee during the civil war when southern troops couldn't get coffee.
Since it was native to Europe and New Orleans was a French port at one time, I wouldn't be surprised if chicory was introduced to the the country through New Orleans. That would also explain the popularity of coffee and chicory in southeast Louisiana.