Libre Graphics World may not update very often, but its articles are usually worth reading. Like this one http://libregraphicsworld.org/blog/entry/document-liberation-project-announces-initial-quarkxpress-support:

Initially, Scribus was pretty much modeled after QuarkXPress, and the two projects still share some similarities. Early in the history of Scribus, it made a lot of sense to introduce support for QXP files. Users got mad with Quark's continuous quirks and bad user support, they would jump ship at the very next opportunity.

Paul Johnson, former Scribus contributor, actually started working on support for QXP files in 2004. But after he had posted to a public mailing list about his progress, he reportedly received a cease and desist letter from Quark.

Scribus was nowhere near its current fame at the time, and even now it would not be able to handle legal expenses (save for a theoretical FSF intervention). Back then Paul just stopped working on that project.

The good news is, Quark no longer seems to be in a position to be such a bully.