This issue has been solved by third-party plugins, e.g. Toolset and Metabox. Both offer taxonomy term custom fields.

While it would be very cool to have such a feature in the core, I also think the developers of such advanced plugins should continue to be able to profit from their hard work. They also contribute to the success of WordPress and play an important role in the ecosystem. If the core incorporates too many of their features, they might lose customers, which would not be good for the ecosystem.

Anyone with more advanced requirements can simply extend WordPress with Toolset or Metabox to have a powerful CMS. Personally, I prefer WordPress + Toolset or WordPress + Metabox to Drupal...