I understand the DT system to work with trust and reputation of a user in the forum that makes other DT members to include them in their trust list and even though some users earn trust due to the assessment of their past behaviors to their present but i think that an inactive DT member should be removed because if a member can stay out of the forum for over 5 years, what will be the probability that they will come back to the forum someday and still maintain same level of reputation that got them trust from some DT members? Perhaps, 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.
If it were about DT1 members, I would agree that only active DT1 members should be elected. In the case of DT2, I don't think there is any urgency to exclude them from the default trust.
The issue here is basically a matter of trust . A user can include another user in the trust until he is not involved in any scam or abuse. In this case, I don't think it matters whether he is active or not.