Why does the talking doll require atunement?

talking doll

To limit the Magic Item to one user instead of letting the whole party pass it around? Or because it's meant to be your beloved toy?

It was the same in XGtE as well.

I think some assume a certain amount of hijinx is possible. For example if a lie is told, doll says "thats not true".

I dont know if thats rules as intended, but the rules as written for the doll are simply that yoh define a "condition" and if that condition is ever met, the doll says the predertimined phrase.

There isnt any stats for the doll for perception or insight or anything like that so one could possibly argue that the doll basically has "perfect" perception and if the condition is true, no matter how hard it would be for a creature with a stat block to detect it, the doll infallibly detects the condition "because magic".

If thats how it works, thats easily worth an attunement slot.  I think id homebrew that the doll's creator's arcana skill becomes the default skill check for all.condition detection checks. And assume normal vision plus darkvision to 60 feet or something.

It's so you know your secrets are safe. Unattuned dolls tell no tales.