The memorial is one of the few flat paved surfaces in the area. The rally was held in a natural amphitheater along the waterfront. The area, like the local media, is on grass and slanted. The memorial is right up against the hawthorne bridge.
They could have done a lot better job, they could have been more sensitive. But that is the most logical place for that kind of thing.
Incidentally, the place was still a mess a week afterward.