Popular opinion of decks usually changes with the release of new booster packs which release a lot of new cards. I think the main issue with Dark World is that while it is great for spam summoning monsters, it has a much harder time destroying enemy monsters with the availability of effect-counters. The ability to destroy enemy monsters without actually attacking is a vital part of Dark World which requires many more spell/trap cards. Having to add all these extra cards means less room for cards that are now considered to be structures for all decks.
tldr; Dark World is becoming to hard to pull off with newer cards.