Likely due to reporting. It seems that news articles are used as the source. If the DJI marketing team maintaining this map is English, it's probably easier to find or verify English news stories. Most fire departments in Belgium now have a few drones as part of a pilot project, and I found a (Dutch) news article of an incident last month were they were used, even though the map is blank for Belgium.

I doubt _all_ rescues that involved drones are on this website. It clearly serves a promotional purpose and the builders of this platform might have more connections to people in the UK who to some degree participated in these rescues.

I can think of a few factors that might be relevant.

British police have been enthusiastic adopters of drones due to ongoing budget constraints. Drones are a lower-cost alternative to helicopters or large search teams.

British geography is well suited to small quadcopters. Helicopters or fixed-wing aircraft are much better suited to SAR operations in large unpopulated areas, but a quadcopter is often a better solution if you're searching a small area with dense terrain.

Britain has an exceptionally large number of CCTV cameras, which has created a base of knowledge and experience in using remotely-operated cameras as part of a search operation.

The Civil Aviation Authority has taken a relatively progressive approach to drone regulation. It's fairly easy to get licensed as a professional operator, and comparatively straightforward for those operators to get permission to fly in potentially high-risk scenarios (e.g. night flying over a densely populated area in controlled airspace).

Part of that could be that emergency services funding has been cut so much that the UK emergency services have to replace people with tech wherever possible, and sometimes where not so possible too. If you can't get 20 people together for a search then 1 drone is the next best alternative.