That's at the equator, because that's where there's the most space. As this thing goes around, there's more room at the equator. Therefore, it goes there less frequently. As you go further north, you see it more frequently, every hour or every half hour or so. And with ships travelling at the speed they do, that's more than adequate to manage maritime awareness and maritime safety.
On May 11th, 2009. See this statement in context.