How do you know that the people in charge didn’t check?

Because the letter we both read says so:

Audits will be conducted in some of the most scrutinized states, but in key states they will not be conducted in a timely way that could reveal any concerns with the vote count. In addition, in most states the audits are insufficiently rigorous to ensure any potential errors in tabulation will be caught and corrected, and they cannot be considered a safeguard against the security breaches that have occurred.

Given these facts, the only guarantee for rigorous, effective audits of the vote in the swing states will be through candidate-requested statewide hand recounts.