Lanefan
Victoria Rules
There's less mention of it in "official" sources for a few perhaps-cynical monetary reasons:Its not just the adventure paths. That's just an external example that can be pointed at. But as I followed the hobby over the years, I saw less and less mention of what would be considered sandboxes anywhere, and I think I saw enough to at least be as representative as anything anyone could see, and more than most have.
--- sandbox campaigns are most often homebrew (can't sell any setting material)
--- there's been very few sandbox-style published modules* in the WotC era (path-style modules sell better)
--- sandbox campaigns have more potential to last longer than path-style campaigns (less campaign turnover means less likely to update to every new edition)
* - is Madness at Gardmore Abbey the only one?