Think of it as a creme brulee. We live on the little hard crust on the top. And there just happens to be a little bit of water on that crust that covers the less-elevated parts.

Now, a little more technical, the crust that makes up the continents and the crust that is under the deep oceans are actually compositionally different. This is because the magma that solidifies to form each of these crusts travels, by partially melting its way up, through different materials and different thicknesses. The consequence of this is that the crust making up the continents is less dense than that making up the bottom of the oceans.

The image above shows the process by which we get new (left) oceanic crust, (right) continental crust, and (middle) a special type of crust like that in Hawaii. Note that when two tectonic plates collide, the more dense one will tend to subduct under the other.