I mean one can reasonably assume they could rest on a mountain if neended no where to take a break in the ocean

Nobody is suggesting that they should rest on the ocean!!
They can´t even rest on a moutain!! So i don´t realy understand this comment!

I mean you say it makes so sense to be able to go over mountains and not oceans.

I'm saying that because the map movement is an abstraction of travel they aren't literally flying non stop a tile would take more then a day to cross. Even if the unit can't stop on the mountain in the map in a less abstract sense after each day or traveling they would need to set up camp and a mountain that's still a possibility, but there is no place to set up a camp in the ocean.

??? Are you real? This is not a metaphysical problem!!!!!
If the unit has the range, it shoud be able to move over ocean tiles! Nothing more, nothing less. Other games like civ don´t have this issue!

The issue here is that ocean is strictly impassable terrain bar the one faction that specifically allows to cross it via the coral that need to expand into it first.

Flying units could maybe be able to move over ocean tiles as long as they end their turn on solid ground, but this sounds like a lot of coding hassle for little benefit.

I was giving an in universe explanation for a mechanics decision. The water are meant to be an ever changing wall over the course of a game with the only way to ever move in them is with the aspects coral. By keeping it that way you can force tactical and strategic decisions with those water tiles in mind while protecting the special ability of the aspects to keep them more unique.

In the lore the water is wild and there are mega monsters in the ocean. So it makes sense that nothing can cross the ocean