Because this is an incredible way of exerting their total control over the web across all browsers. If they don't like a feature, they get to downgrade the user's attestation or fail it. If it costs them some unattested traffic in order to create a permanently unassailable market position, it's worth the money.
It'll block all other search engines by preventing web scraping except those blessed by Google. For this reason alone many websites will adopt it. This will impact competition, research and freedom.
After this, all user choice is gone, and it'll only be governments who can break the racket.
If the CCP don't already do this, I expect they'll quickly implement something similar.