(There are many members who remain DT2 that are no longer active)
It’s to protect the account in case someone might hack it since Zepher will never come back again which means his DT position has no use anymore. His trust feedback is still reflected on every user profile that he has past trade.
To do this it makes more sense to leave feedback on the account stating that the user has died, either in neutral or positive, so that if the user wakes up it won't take long for someone to raise the topic.
Can't think of many examples right now but Tecshare comes to mind. RIP based feedback was left on his account, but no-one left negative because he had died. Furthermore someone's feedback doesn't become useless if they leave, it's still just as useful even if it won't be updated and therefore can become outdated. Many DT members have otherwise left but there feedback remains trusted.
The case with Lauda wasn't the same as either Zepher or Techsare. Lauda left and made it clear that any activity from her account should be considered an imposter, and therefore not trusted. That was a good enough reason to get tagged as a warning to others, because that also seemed like what she wanted, not simply because she was leaving. It was a very unique situation imo.
More relevantly though, it's not accurate to say that many removed Lauda from trust inclusion after this, not based on the logs provided. She had already become excluded from DT for the best part of 6 months and remained on and off after for almost two years, until as recently as August last year. Within a week of saying goodbye she instead went from -1 exclusion to 0 (inclusion). You could point to her getting to -7 the following year after leaving, but she had already reached -13 in the year she left prior to leaving, so I don't think her exclusion is that related to her leaving, as her feedback was already in general distrusted by then.
Unfortunately there are many misconceptions about Lauda's exclusion from DT, I'm not surprised that many people think it's because she left and requested to have her account distrusted. If anything the opposite could be true. After years of being a DT members and tagging thousands of scammers she had become distrusted, and therefore left the forum as her work had gone to waste.