An obvious answer would be that archaeology started in Europe. There have been more surveys there over a longer period. Egypt is well-represented because huge pyramids are hard to miss, but also because of European (and American) obsession with Egyptology in the 19th and 20th centuries, which led to many expeditions and digs that found or dated many of the entries on the list.

The British Isles is incredibly secure in a geological sense. No volcanos, no major earthquakes, a few relatively weak tornadoes and every couple of decades a hurricane that's already lost most of its puff. This reduces the risk of damage quite considerably. Same with Northern France. But as you reach the Mediterranean, you have volcanos and earthquakes. You also have civilisations like Rome which may have incorporated older structures or built over them or destroyed them. Britain remained relatively undeveloped until the 19th Century, and for a long time any new construction has required a comprehensive archaeological survey of the site.

Hi, while this question about prehistoric archaeological sites may get answers here, it would be worth x-posting to our sister sub, /r/AskAnthropology. You might also consider /r/Archaeology or /r/AskScience.