Tor.com posted a lengthy interview between Tor publisher Tom Doherty and Harriet McDougal (Robert Jordan's widow, and the editor of the entire Wheel of Time series). They cover many topics ranging from their approach to marketing The Eye of the World in 1990:
Harriet and I decided we were going to make [The Eye of the World] a bestseller. We did it in trade paper because we were afraid we couldn’t get enough out of a fat hardcover book. Trade paper wasn’t anywhere near as big then as it is now, but we thought that’s good, too, because it will call attention to itself. It’ll be different. So we did it in trade paper and sold 40,000 copies, which was huge for trade paper in those days, for the first of a fantasy series.
[The late ebook release] wasn’t a selfish reason. The brick‑and‑mortar bookstores were very good to Robert Jordan throughout his career. They are having a hard time now. This was a chance for Robert Jordan to give back to people who had been very good to him for 20 years. That was really the main reason for the windowing.