“Worlds largest coal port” should be specific enough, surely.

It’s not the direct effect of delaying a few ships for a day, it’s the media coverage. Rising Tide has become a well known protest in Australia and it gets international news every year.

Also - possibly most important - it helps get on board the people who complain about climate protests disrupting “ordinary people” instead of the fossil fuel corporations directly. It’s much better PR to be seen to inconvenience the conglomerates.