I think one of the main draws of Gamescom has always been the community or interactivity, also Köln is in the blue banana of Europe so there’s probably almost 100milion people within a 5 hour drive. I don’t really know why E3 is failing but I can roughly tell you why Gamescom isn’t, for one while there are occasional issues Orga is good generally, half of the German media lives a stones throw away from the fairgrounds, a lot of entertainment is provided besides the fair itself (concerts and other things throughout the city), it’s organised by the German games industry association so the cashflow required could be more easily acquired, it also likely means more stability, the city and potentially the entire country want the event to succeed which likely helps. Most of this is just educated guesswork though so take it with a little scepticism.