Warframe has a pretty good ship interior, simple and functional, nothing complex for a small upgrade. I don't understand people and their lack of creativity. I just showed a game made by a single human with a lot of creativity, I can't accept that a whole company with a great team is paying them to do the bare minimum.
Things are not that easy.
I have no clue about Warframe. I don't even know what kind of game it is - do you actually fly a spaceship? I could not find anything coherent, seems there are these things called Orbiter? Sounds like it is a player home, not a spaceship you fly. I can't be bothered to research deeper into Warframe, because I am not interested, all I could find by skimming the internet is how you decorate them, not how you fly them (maybe you don't?); my initial impression is that traveling is an illusion in those things. It is a home that does fancy fast traveling? Don't try to explain, I don't care.
Because all that is beside the point. Just because game A has a feature does not mean that game B either needs that feature or is even able to implement it, or that it is economically viable to put the work into it.
You say the dude behind Spacebourne seems to run a one man show; or maybe he doesn't, he always uses "we", but that may as well be business speak to seem bigger or more professional than his company really is. If he really does it by himself: Kudos, that is a monumental task, but in a way it might even be easier than if you have to coordinate and integrate the output of multiple people or teams. One man shows often produce spectacular results. But also:
Spacebourne 2 is apparently not finished, but goes into early access, and I read a lot of "we have planned". It is not a multiplayer game, so a lot of complications are already off the table. They seem to use the Unreal engine, which is practically made for indie devs like them and single player open world RPG games. Behemoths like ED? Not so much (reminds me, we didn't have a "ED should switch to Unreal" thread for a while). While still being a lot of work they are not developing and/or modifying their own game engine, which is a completely different task. Both engines are very different frameworks and toolsets for very different purposes.
Then it is probably much harder and more expensive to develop games in a studio as large as Frontier as it is doing it indie-style. I would compare that to mod makers. Single mod makers can do some amazing things, and people ask: Why can the developer not do that? Answer: Because he needs to make money and pay its employees. Mod makers work for free. And if a game is old and/or does not generate the sufficient amount of revenue, it doesn't get love or dev time. Simple as that.
How is Spacebourne 2 financed? Is he really doing it alone, or does he actually have employees? Things get more complicated and can move more and more at glacial speeds the larger a company gets. Example: A single indie developer doing a game... well in his basement, to be frank, might be passionate and comfortable to put 12 to 14 hour shifts seven days a week into it. Do that with 800 employees and things get very expensive, become legally troubling or even both.
All that is fine, and one can spin theories about why or why not ED should or should not get ship interiors, but fact is: They are not coming. There are currently no game loops for it, so ship interiors by themselves are a waste of dev time just for decoration, and, most important, Frontier said no.
Not apologizing for them, just saying: Get comfortable with the truth. First and foremost it is probably just not economically viable to invest into ship interiors. End of story.