The largest Pictionary-like web app for the good part of a decade or so (early 2000s to early 2010s) was a Shockwave/Director app. Newer clones are yet to match its amazing features. Unfortunately isketch.net got too old for the newer generations to pick it up. I can only guess what happened to the site. The technical debt must have been too great to port it to a newer platform, or perhaps the devs/maintainers moved on.