Only 6% of the ocean floor has been mapped. People at the Seabed 2030 project plan to map the ocean floor in high res by 2030.
Reasons to do this include navigation safety, ability to lay fiber optic wire and pipelines, because we don't know what's there, weather forecasts since water/temperature flows along ocean floor contours affect atmospheric flows, tsunami predictions, we could find sea wrecks.
Another thing that fascinates me are seamounts: volcanoes that either didn't reach the surface or that did but later eroded and subsided. With sea levels 100-150 ft lower in the last ice age, many eroded to that level, leaving a flat-topped mountain that far beneath the surface. It's too deep for normal scuba, but amateur underwater drones could easily explore them.
Secondly, no scuba diver is about to dive on the ocean floor. Maybe you're thinking of deep sea divers, who dive in a submarine or other deep sea vessel?