Not sure why they would bring cost as a reason. The 5km and 10km courses are there, it's just more laps (yes sometimes they use a slightly longer course, but if the cost of some extra buoys and officials is really too much, just use the same course). It would be like cutting the 10,000m in athletics and citing costs as a reason.
Personally I feel participation is at an okay level, definitely not enough to be considered for the Olympics, but enough for World Championships. Especially since it's at the same level of some diving and artistic swimming events.