It's not as if it requires the same resources to create gathering spots as it does to evaluate player complaints, or balance gear and difficulty to make a new instance. They have an artist or two on staff, the artist made this, they might as well put it in while the designers work on whatever it is they're working on.
Making the actual art for new content is probably the easiest part of making new content; I'm sure that there are already several instances with completed art, waiting on boss and equipment balancing.
Making the actual art for new content is probably the easiest part of making new content; I'm sure that there are already several instances with completed art, waiting on boss and equipment balancing.