Also, it may be just a matter of getting used to, but I found the color of the heatmap to be a bit misleading. When you switch to a specific activity - for example, night life, the high concentration areas are in red, while that color means low concentration when on the Liveability tab.
The coverage is larger part of Europe, gaps are present where there are no data points, where OSM coverage is practically zero. Aremenia looks like it's on a cut off border of OSM Europe file that's the source of everything here, only points close to the border are available.