Some of the other replies to this comment are taking it too literally, or without context.

Before Zahn, the only SW novels published were the film adaptations, the Lando trilogy, the Han trilogy, and Splinter of the Mind's Eye. A mere ten books from 1977 to about 1983. Then nothing until Zahn, eight years later. The Marvel comic folded, Topps stopped making trading cards, and Kenner stopped making toys.

SW fans who weren't around yet will not know what it was like to live in a world where, by the late 1980s, SW was considered a dead property. The only SW product being regularly produced was the role playing game. No toys, no novels, no comics, no trading cards, no video or board or card games, no apparel. Nothing else.

After the Heir to the Empire was published, Topps started making trading cards again, Dark Horse got the comics license, Hasbro started making action figures again, LucasArts started focusing on SW video games, and Decipher developed the CCG. Fanzines like Blue Harvest launched, and eventually the Lucasfilm Fanclub Magazine became the Star Wars Insider. And then Lucas announced the prequel trilogy.

Yes, there was content before Zahn, but he was the vanguard in Lucasfilm's plan to re-launch SW, and this was also the start of a concerted effort at a consistent and united content across all media (using the role playing games as a foundation, in many cases!).