There’s some selection bias here — the tweets we see in the thread are the ones twitter didn’t remove and the accounts twitter didn’t ban.
Twitter surely has the deleted tweets around somewhere, but it doesn’t seem to have been provided to the twitter files reporters.
Twitter’s internal tools still have all of that data. In most cases the Internet Archive also does, too, which is how people have confirmed that, for example, the tweets in the famous “handled” email were nudes in violation of the non-consensual policy with no overriding news value.