This is a really interesting question, especially considering some of the historical context to manned underwater exploration. I'd argue a large value from manned exploration comes from the physical act of placing a human somewhere, similar to the case with many of our missions to the moon. Society seems to gain a new appreciation for what we have available locally when we send people to far off, unexplored places. Missions to the moon jump-started a space race that, with a few faltering decades, we are only just beginning to see come into maturity with companies like RocketLab and Spacex. The United States Navy tried initiating a similar race to the bottom of the ocean with expeditions SEALAB I and II, but those efforts eventually failed. The deep ocean is more abstract to society, we don't see it most every night as we do the moon, and so it's more difficult for it to inhabit our dreams of the future. I don't know what the world would look like today if we had a "sea race" similar to the space race, but I imagine we would all have a better understanding of the importance of the deep ocean and value it a bit more than we do currently. I don't think you'll see those attitudes develop in society until a new generation can grow up reading stories about the first man/woman to stand at the marianas trench, much like what happened for moon exploration.