Having said that, I wasn't the one to mark any of the reports bad. In fact, I left the one's which did have replies as a soft bad, by just leaving them unhandled, because I can see it from both points of view. The global moderator who handled these reports, must have thought they could've been significant to the history of the user, in some way I imagine.
Generally, we don't allow users to remove their own threads, and I guess this could potentially be abused, and whoever marked them bad could be thinking along those lines. However for me, since there was no replies or any trust references/flags left on the one's I handled, I thought they were insignificant enough to be removed. Maybe, whoever handled them had a different point of view to that, however it depends since the examples you've given all that activity from other users.
Also, the user in question has clearly tried to hide his post history. Now, there's nothing stopping users from doing that I suppose, but they can't remove the threads themselves. I usually, weigh this up, and generally if the threads don't have any replies, and they've been inactive for years, and has no scam accusations or trust references left, I usually remove them.
https://bitcointalksearch.org/topic/m.36587529
https://bitcointalksearch.org/topic/m.36588874
https://bitcointalksearch.org/topic/m.40145465
https://bitcointalksearch.org/topic/m.36582223
https://bitcointalksearch.org/topic/m.36555924
Here's some examples where keeping these around might be a good idea:
1. Users that want to research old projects that they had interest in
2. Scam report, multiple years after
3. Users who've asked substantial posts, when at a time the thread itself was substantial enough getting punished by the thread being removed. Since, technically most users wouldn't be bothered by this thread since they'll never stumble upon it, I think it feels a little harsh on the users losing posts because of it
4. Anything with replies from users generally isn't removed.