When the “relationship” is 100% dialogue, that is enough for some young or impressionable people to form an attachment.
It’s an artificial attachment, because the human is choosing what kind of responses they are likely to get. Very little is left to chance or spontaneity. A verbal robot that “speaks” with expression and enthusiasm, if you want it to.
A verbal robot that supports and defends whatever you say.
We want a “yes person” around to affirm our position.