Google's layoffs were not a result of necessity, but rather a result of leadership's concern about the accumulation of unnecessary projects and underperforming employees during good years.
This temporary fix poses unnecessary risk and could jeopardize the company. Attempting to reinvent or replace online ads for user benefit could potentially destroy the entire business, and poses significant regulatory and PR risks.
Google would not be able to pull off something like TikTok without facing backlash from regulators and journalists. The same applies to ChatGPT.