Jules Verne was way ahead of his time. Sure, all good sci-fi authors are a little ahead of their time, but Verne was way ahead. In From the Earth to the Moon, for example, he predicted manned missions to the moon over a century before they actually happened (though he was a bit off about what we would find there).
Verne's time has come and gone, though. We've been to the moon, and brought back souvenirs, and that was long enough ago that most people aren't old enough to remember America's finest hour. We can get around the world in eighty hours without too much trouble save jet lag, and we have satellites that can get around the world in eighty minutes, or even less. The Journey to the Center of the Earth might seem like a silly adventure story these days, but only because we've mapped out the tectonic plates, and know the composition of the Earth all the way to the chewy center.
And yet, it seems like there's still something missing. In his 20,000 Leagues Under the Sea, Verne painted an astonishing portrait of the world beneath the waves. (Disclaimer: I read the book in the third grade, so my recollection of it is a bit hazy, so I won't be going into specifics.) Somehow today, nearly a century and a half later, we haven't significantly demystified the ocean since the day the book was published. If anything, the decline in sailing since then has actually remystified the oceans for the majority of people.
Why haven't we explored the ocean thoroughly by now? There's the obvious problem with putting stuff underwater; waterproofing everything is kind of a pain. You also have to take into account human factors. Fundamentally, we're a land based species, and we'll probably never feel totally comfortable underwater. Still, both of these are pretty unsatisfying reasons. There's no fundamental reason for us to avoid exploring the ocean. All of the obstacles I can think of are eminently surmountable.
One of these days, we're going to colonize the oceans. Building stuff underwater may be more expensive, but right now we have a finite amount of land, and exponential population growth, and one day the benefits will outweigh the costs. It'll probably start near densely-packed urban areas that are on the water - Manhattan, Singapore, a couple places in Japan. (Come to think of it, I wonder who owns the offshore property rights?) When we start moving into the sea, we're going to need a much deeper understanding of it, both scientifically, and informally for the average person living underwater.