Because it works. They are designed to simulate human conversation. They are great at repeating/summarizing and reframing situations and empathy- skills of a therapist. Since they know resources, the validity of coping techniques and other suggestions the possibility of the responses being AI hallucinations doesn’t really matter because they are easily tested for practicality by the user, once given. And we can logically test many AI suggestions in our heads to easily determine their validity.
I switched from depakote to Zyprexa because I was gaining too much weight. Olanzapine still makes you hungry but less than depakote. I gained 40 lbs on Depakote. I gain a pound or two every few months with Zyprexa. I switched to one meal a day though with a healthy snack in the morning. Manage weight better from medication side effects with a water flavor-sweetener. When you are hungry, take a sip. Helps for hydration and hunger at the same time.