As others have said, it was originally designed and implemented for Avatar gameplay back when CCP had dreams of turning Eve Online into a Virtual Reality SyFy game.
Creating the Character Customization was the first part, then implementing Captains Quarters was the second part. The third part was to implement gameplay content for Avatars.
However due to lack of viable tech to make that content work and because of overwhelming opposition from hardcore PvP spaceship fanatics, CCP shelved that work and then eventually canned it.
It’s a shame they removed Captains Quarters, they could have done a lot more with it without actually involving other Avatars. Such as being able to customize the interiors, add some action scripted pets, etc. They could have opened ‘The Door’ and added an elevator so Avatars could go down to a sub-level maze of hallways where ‘Undercover’ Agents were located offering special in-station missions, requiring Avatars to open locked doors to rooms with locked containers that could be hacked open for access to loot and mission objective items.
The possibilities were endless, definitely a missed opportunity to expand the game and increase player subscription numbers.