Actually the majority of the marinas we frequent are quite diligent about watching for any type obstructions on docks. There are many elderly persons frequenting them in addition to people carrying things and not looking. And, the marina has quite a bit of liability. Now there are the exceptions with lines, fuel hoses, electriccables and a bit of every other obstacle they can imagine on the docks.
There are liability issues in the US. These kinds of things are accidents and lawsuits waiting to happen and any good marina would like to know which of their employees is trying to put them at risk.
I think you are doing a good thing by letting the marina/yard manager know what you found. You weren't injured and neither were other folks but someone really could have been especially carrying something heavy in front of you without the ability to see well ahead.