Trusting the user does not transitively extend to the software they use. You might be OK with them e.g. looking at company financials, but you'd really like to be sure e.g. that the syntax highlighter they use doesn't go and exfil that data. You still want them to be able to use the syntax highlighter. (Yes, it's an obviusly made-up example_

You _can_ fully vet apps, each and every one. Or you can choose a zero-trust approach and only vet the apps where it's necessary to extend trust.