Although the typical SC community is keeping Brood War alive, I have noticed a substantial decline in Starcraft map-making, which is one of the reasons I abandoned it. This might be for a multitude of reasons:
1) The introduction of the Warcraft III editor took a chunk out of the SC map making community. I know, since my clan lost half of its members to it.
2) Most of the limits of the Campaign Editor have been discovered: square terrain, altering doodad states, player colors, overlapping, etc.. it becomes a bit old once all of the secrets have been discovered.
3) I think a lot of good map makers are discouraged from making maps due to the popularity of shitty maps, such as mass attack maps and cliche defense maps. There is a major lack of innovation.
4) This isn't really a reason, but when I left Sc, most of the well-known map making clans, including Mp) and (U), were decaying. A mark of the apocalypse, no doubt.
5) And, Warcraft III and WoW in general have helped to kill the SC map making community.