Why? Unless the thread is asking a technical question, it's less likely than not to have been resolved.

People wouldn't return to necro'ed threads beyond the initial bump post alone if there was nothing of relevance or openings for ongoing discussion in the original topic (or its tangents as the thread evolved).

Should we instead just be sure to open up new threads for each otherwise ongoing discussion just because another LL's silence or obfuscation left its posters disheartened for the time being? That would seem to go against the suggested practices for these forums...