Before the 00s, it was coated with a substance called Quilon. Then they switched to silicone.

Yes, one of the people who helped popularize it was Julia Child, I believe starting with her hefty book Mastering the Art of French Cooking in 1961. We had that in hardcover in the late 1970s and 80s, heavily used in our kitchen. I used to make its crème caramel, although that didn’t involve parchment paper.

Later her TV show The French Chef apparently also popularized it further - it ran from 1963 to 1973.

But, searching the subject it seems that she helped popularize a technique in 1997 on her later TV show, Baking With Julia, in which you use an upside down pan as a guide to cut a perfect circle of parchment that fits the pan. Perhaps that helps explain more widespread awareness in the 2000s?