I don't think that's the main problem. They wouldn't invested money into Google Assistant, which directly hurts Google revenue. They also already give direct answers to questions on Google without ads.
Realistically, the main problem is scaling and costs/benefits. You have to remember Google is accessed by billions of people a day. Now imagine they serve a product like ChatGPT. You would be pissing off a lot of users with a product that is laggy, often crashes, requires a hourly rate limit just to protect your business from going bankrupt on computing costs. It's not really beneficial to Google to rush a model into their golden product that isn't ready for the scale it operates at.