At youtube's ad income rate (~$13/year), the current (but growing) ~800 million chatgpt users would add ~$10 billion. At facebook's rate (~$40-50/year) $32-40 billion. Potentially, an assistant would be more integrated into your life than either of those two.
The "audience retention" is the key question, not the profitability if they maintain their current audience. I've been surprised how many non-technical people I know don't want to try other models. "ChatGPT knows me".
The same isn't true about ChatGPT.
Anthropic and Google provides a similar product, and switching to a better/cheaper platform is fairly easy as it only depends on you and not on others (content creators or friends) doing the same.
And this is definitely not happening. They are covering training costs with investors money, and they can't really stop it without their competitors catching up