Okay okay - maybe someone has already mentioned this, but here’s a Nevermoor-theory!
WHAT IF the reason why Deucalion seems to like Morrigan sooo much is because it’s a Wundrous Act? It was created by a Wundersmith - as a hotel or something else - before the Courage Square Massacre.
In the books, it’s mentioned a few times that it’s in Morrigan’s (a Wundersmith) favor. It does whatever it wants to please Morrigan - from creating a room and designing it the way she likes it, to being willing to do things to make Morrigan stay and cheer her up. Ex. cheering her up by creating her favourite smell in the Smoking Parlor when she was low.
As well as (if i remember correctly) in Silverborn, it valued Morrigan’s wish to have some privacy/seperation from Jupiter. Literally throwing him out if the room when she needed to have some space!! Not to mention the way it became soo depressed and sad when Morrigan was staying at the Darling’s, doing whatever was in its power to make her stay.
It’s been mentioned quite a few times that it’s got a mind of its own. Even though Nevermoor is a magical place, it’s hinted that there’s not a lot of things that are magical without a reason. Without a magic-caster. Such as the jumping-things Louis and Lottie used in Silverborn (which was also created by a Wundersmith, if I remember correctly?).
It’s also mentioned throughout the books that Deucalion seems to value Morrigan’s wants and wishes more than it values the wants of other’s. As mentioned previously, even above Jupiter.
Could it be that it favor’s Morrigan’s needs because she’s a Wundersmith and it was created by a Wundersmith a century ago?????