has a person who does 3d rendering it is a whole lot hard to get a water mesh working right. the meshes themselves would be over Quads that means there (1 big square poly that is then spilt many many many times over) and the shaders would of course be layered to make a movement. ask any pro 3d renderer about making the ocean and you get a long list of why they don't fancy doing it.has you then have to animate it. using the x/y/z axis that would make it Time consuming on the engine and your machine.
Its even besides the point. Planets with thin atmospheres are targeted first. If they had not done that, they would have had to come up (knowing FD) with a plausible weather system based on the size and mass of the planet, distance to the star, axis inclination, availability of moons, binary (or more) companions and what not. So thin atmosphere planets. Oceans can't exist on planets with thin atmospheres, or it would be a planet with a thick atmosphere, or they would have evaporated.
How can it be difficult to develop...
It's not easy, but it makes the worlds more interesting.
I really have no idea what you are trying to discuss here. The OP is thoroughly founded on "Duh, how hard can it be?", and now it is not easy?
After 5 years, if you still can't see the conceptual differences between NMS and ED, and keep comparing the 2 with each other (which is your prerogative), you might draw the conclusion you will always be disappointed in what ED will become.
NMS doesn't give a crap about walking hamburgers on 6 legs, so why should it take evaporation into account? It just is there because it looks nice. I'm soooo glad FD took a different route.