Difficult to see, very expensive to maintain.
Not always - recall night flying in the 1960/1970s and Birmingham was one of the best which on a good night could be seen circa 30/40 miles away!
They come from times that predate modern navigation systems and the reliablity (!) of both airborne and ground communications, not to mention items such as SSR.
I only remarked a few weeks ago when northbound passing the Channel Isles on a clear night at FL 360 how one used to be able to see all the marine lights/lighthouses etc in the "olden days" - it was quite fun sitting there trying to identify them all.