There are probably some minor technical issues which make maintaining more smaller worlds easier, but mostly it's a business format thing. This game is on almost like 30 servers with 100+ worlds totaling. Since the business formula is pay to win, if you have 100+ worlds, there can be 100+ winners, so a lot more people are willing to pay. As compared to let's say how much would #1 player in X-world who has lets say spent 5k dollars in this game, how much would have he spent if he were competing to be #235 or #236 in combined all servers rank. Probably less, so hence the format. Also it allows them to be spread out on different language regions better and also restart the game(which is based on advancement) every once in a while by opening a new world. All and all, it makes sense for this game to be spread out both as a business and as a product. I do think this game has taken it over the top tho, current worlds in different servers feel way too small and very much lack competitiveness.