This is my theory.
Remember the think in McD with granma, the spirit consume "each other", it was the higher one consume lesser one.
I think there is tier or caste in their system,which the stronger you are the more you need to eat(like mcd) OR eat a strong spirit (quantity vs quality)
Thus making me thinking, the shrine(and its monster and attendant) ask a strong spirit as offeering.
Since romm and mieruko have a "gift" to see them(strong one) so the shrine assume they capable of luring them to the shrine.
Which answer some question about romm situation and if you look closely at apartement chapter,when the shrine monster consume what bothering hana,it looks like its "satisfied" for now,but i think the shrine monster kinda want ppl to lure it to them since leaving the mountain strains the big boy