Would anyone trust them to not silently still collect personal data?
For example, even if they don't need the data now because you're paying not to see ads, they might still collect it so that they can show you "better" ads if/when you stop paying.
Disabling ad tracking is not going to change how they scan all the file contents and categorize them using AI. It might be even more effective for them than tracking you on web.
They tried to do e2e encryption with Allo, then they integrated all the crappy smileys from it to their other messagong products, and got rid of Allo.
The scary thing is that in theory they don't have ads on messaging, but if it would be true, they would have gone farther with e2e