And these signs seem very recent. Some guides mention many swimming holes that are now very difficult to access. Some other places had signs from locals to discourage tourists, and while it holds no legal value, who wants to take their chance offending local people.

Maui is however dealing with unprecedented numbers of tourists, and what was once semi-secret swimming holes are now well-known thanks to guides and social media, so it makes sense, there are always those tourists who see a full parking lot (more like a pull-out area with space for just a few cars) and manage to park themselves in a very awkward unsafe way, easier to just restrict parking altogether.