I don't think it's that people want a certain nostalgic UI. It's that most of these applications are built by volunteers, for free, and are already understaffed. From an individual's perspective, it's much more important, and possible, to fix bug #155 or implement a new feature than to try to overhaul the entire UI. In order to do that, you'd have to get everyone on board and everyone would have to agree with the changes. A lot of projects are too flat as organizations for this to go smoothly.