At one point Ebay wasn't so ugly, it was more par for the course. While it was rocketing to popularity it had a simple and clean design (iirc). Of course, since then it did two things wrong:
1) never kept up with current design expectations
2) never really refactored despite a feature influx.
I think everything went exactly right. Most people who use Ebay know it like the back of their hand, simply from experience. Gradually adding new stuff isn't stressful for users, compared to a redesign, and rocking the boat is the last thing Ebay wants to do, considering that their only advantage over competitors or potential competitors at this point is momentum.
1) never kept up with current design expectations 2) never really refactored despite a feature influx.