Google doesn't need to sell it to third parties, because they are the only party they need to monetize your data.

Yet. That we know of. IIRC the way the relevant EULAs are written they could do if they wanted to.

I can't say I've actually read the EULA, but they do have a nice Privacy FAQ, which I assume is nearly as legally binding: https://support.google.com/work/answer/6056650?hl=en

"Google processes your data to fulfill our contractual obligation to deliver our services. Google’s customers own their data, not Google. The data that companies, schools and students put into our systems is theirs. Google does not sell your data to third parties. Google offers our customers a detailed Data Processing Amendment that describes our commitment to protecting your data."

Another way to look at it might be, given your data is one of their biggest assets, it would be foolish to sell it.