...for those who made it clear they won't return to the forum again, what is the essence of still leaving them in the DT? besides, the positive trust feedback from other DT members should be enough.
It's unfortunate that you are seeing it from only one angle, which is the angle of positive trust.
Try to be holistic and rational here; take for a example, a certain scammer is discovered and tagged by a DT member in 2018, and down to 2025, you exclude the DT member that tagged the scammer due to inactive, don't you think the scammer will simply return to the forum to scam?
As others said above, inactivity doesn't render feedback useless whether positive or negative.