Question about Hags

Is there a lore-friendly reason for a hag to raise a captured baby instead of simply eating it to reproduce?

The baby tastes really fucking bad.

Hello.

Maybe the hag wants a servant, or a minion who can walk among civilized people. Or perhaps the hag is bound by a debt to raise and protect the child.

I'm bored and lonely. Fuck it, I'm making the next magically attuned baby an apprentice. At least then I've got more to talk to than my familiar.
Oh hey, this one is magically attuned. Now.. what do babies eat? Guess I'll just try a bunch of stuff, and if it dies I'll eat it and make the next viable baby an apprentice.

Gann wasn't kidnapped, though. He was a hagspawn.

I like this one.

"Nanny Bonegrinder, why do you have ten fingers and I only have nine?"

"Nanna had to make sure you weren't a cookin' babe sweetpea."

This, it wants a catspaw.

Conceivably, if the hag was commited to ruining the parents life, promising them that she would raise the child to become a malicious sociopath could be one of the worst punishments imaginable.

Boredom.
Loneliness.
Want for a loyal apprentice and/or little helper later in life.
Ease of adopting compared to having her child. Some vestigial remnant of maternal instinct from a time long since past.

Pick any combination, You want OP. I'm assuming your going with a setting where hags are living creatures like everyone else, and not just manifestations of nature's cruelty, because if it were the latter, you wouldn't even need to bother asking the question, or any question actually, on how it would act.