Successfully implementing ship interiors the way players want, that is the way Star Citizen does, is far harder than it appears to the average player. There's a reason Fleet Carriers make you all sit down in a seat before jumping, because what people want is not easy.
Going to echo this comment because it's effectively the reality.
We would already
have ship interiors if it was within Frontier's capability to do, with the resources and time they have available. I think people forget that the Elite Dangerous development team is orders smaller than CIG's development team. Frontier is also operating with a much smaller community of (active) players (and by extension, funding; adding something as massive as ship interiors is potentially a multi-year investment needing a lot of dedicated resources to build the entire capability, across multiple disciplines).
The reality is, nothing short of the fully interactive, full nav-mesh, physicalised ships - down to cockpits, components, cargo spaces and so on - would be accepted. We all know this. Frontier knows this. There is no middle ground; anyone suggesting there is, is being a little bit dishonest (and it's just special pleading to argue such).
As to why? Time, resources, intent. The first two are very likely to be the key reason. The third is really a value proposition, for a very long time, Elite Dangerous was an investment source for other IP development; that's not actually uncommon, for one game to help fund another and it's allowed any number of excellent games to see the light of day as a result. It's also a double edged sword in that a pretty large number of subsequent titles have failed, to one degree or another (something Frontier has also experienced).
The amount of time and resources needed to rework multiple ships, however, developing the architecture to have ships be a navigable space, the massive amount of things that need to be physicalised, building all the navmesh and interactables? Odyssey shows the engine is capable of quite a lot, but also some of its limitations. The Cobra engine would not make it easy on Frontier to implement.
Asking for interiors for ships, is akin to asking Frontier to ground up rebuild the game. That is what it translates to. Genuinely. It's that big of a deal. And that is why they haven't happened, basically. I am without any doubt at all, Frontier would like to add interiors. But wanting to, and being able to, are two entirely different things. So they focus on other features, instead.
Star Citizen is such an incredibly delayed, buggy, beautiful mess of a game,
precisely because Chris Roberts keeps saying yes to every idea imaginable and whilst it's finally starting to show some promise, is likely a decade away from being a game and not just a large number of different and mostly disconnected mechanics
.
There is something of a cautionary tale, there.
Lastly, I would very much like to see interiors. I firmly believe it would 'finish' the game in ways nothing else ever will. However, I recognise the costs and risks Frontier face, to implement it. And so I don't keep
endlessly asking them to do something I know they would do, in a heartbeat, if the opportunity arose. I don't think it's ever been something that isn't the top requested feature, for the 11+ years that ED has existed.
