Going off of other tumblr posts about humans being survivor space orcs and humans being loving frienddog pet buddies to other alien ships, what if the ability to attach to things was a trait of earth critters.
As long as a behaviour helps achieve the same end, evolution doesn’t care what the behaviour is. So you get both bats and birds with entirely different structures, methods, and styles to flight for different niche purposes (long distance vs. nimble acrobatics) but they both succeed at flying. The same can happen for social structures and space travel.
For most other life in the universe, social bonding isn’t a thing. You get people that you get well along with or don’t. Property isn’t necessary if it doesn’t have a function, people don’t get attached to objects. People strive to increase their station/power and therefore overall happiness, whatever that means to them, which is what encourages a group of them to work together for efficiency and shared earnings. (For example, that is. There are lots of things that could encourage life to reach spaceflight. Like spite. Or blind chance.)
On earth a few animals have evolved favoritism behaviour. Getting attached to objects, other animals, and ideas for no reason other than they like them. This helps ensure the survival of a group, so it encourages repetition. Humans are the only spacefaring creature that has favourite ROCKS because of this. Imagine having a favourite pebble out of the entire universe full of mineable minerals!
It’s just common sense that if you want to survive, add a human to your crew. Because of the space orc endurance toughness thing, being able to survive things others can’t, and being determined to keep going. Combine that with the happy space dog thing where, essentially, you put a Kirk in with a hundred Spocks. The dog Kirk is the one who’s always happy to explore and meet people and make friends and likes everyone. So if you have a being who enjoys your presence for no material reward AND extends their instincts for survival to things they’ve bonded on, you’ve basically got a big bodyguard for your entire crew. For free. You don’t have to pay it. You just have to say ‘thank you’ when it gifts you useless trinkets it found or made.
So you get these ships, and you can always tell which room is the human’s room. It’s the one full of hoarded junk. There’s sheets and dry film stuck to the walls that it ensures you is coded with dyes to make a message. The message isn’t really important, just nice. The human likes it. The human collects lumps of polycarbons that it tells you represent icons of aesthetic and memory. You don’t understand, because your memory works just fine without a visual reminder, but you learn that apparently there are different kinds of lumps and they mean different things.
The human has clothes it prefers when all its body coverings function about the same. It has days it prefers. It has abstract concepts it prefers. It has noise it prefers, and carries the noise around with it.
How would that affect a creature that prefers nothing? A species that constantly strives for a better station would have ambitions and goals for being transported to higher ranks on better ships. Logically, it would also prefer the smartest, strongest, nicest humans to protect their investments. A creature like that would check the stats on available and working humans for hire and want the best one they can afford.
But if you asked a crew which human they would want to work with? If you give them enough time, they’ll start saying their own.
“But isn’t the one on ship 4-aNui 0.93s faster at achieving the emergency fire plan escape?”
“Yes, but ours likes us more and would be more efficient at helping us, specifically.”
“That’s what humans do. They’ll like anyone they’re introduced to.”
“Yes, but ours likes us.”
“The better one will like you too if you give it enough time. I thought you knew this?”
“But I like it.”