Many of them have been upgraded. In the US, we've replaced HOST (the old ATC backend system) with ERAM (the modern replacement) as of 2015. However, you have t

Many of them have been upgraded. In the US, we've replaced HOST (the old ATC backend system) with ERAM (the modern replacement) as of 2015. However, you have to remember this is a global problem. You need to maintain 100% backwards compatibility with every country on the planet. So even if you upgrade your country's systems to something modern, you still have to support old analog communication links and industry standard data formats.