All decisions are based on a majority vote (aside from obvious minors, spammers and temp thread closures/removals) so there is no way I can sit here and give concrete reasons for each of the examples you give... I honestly can't speak for any other member of the team and tell you why each one voted a certain way on a specific report.
What I say is this:
1. Starting a thread does not give you ownership of the thread, the right to dictate the direction of the thread, or the right to demand it be closed.
2. Not all derailments are a bad thing, neither do they require our intervention.
3. Not all derailment reports are actual derailments and are more about people being pissy that they can't control what others think about the topic, or the natural direction the thread has taken.
4. We have a precedent for closing threads of this nature (the ones mocking RedDude) dating back a good 5 years, possibly more but I can't be sure as I wasn't a moderator prior to that.
5. Fleshpiles are a long standing and sorely missed tradition for LPSG - We should have more of them, in every thread going!
6. A lot goes on "behind the scenes" when we get reports, you aren't always privy to the full picture of what has and hasn't been done by ourselves or the members partaking in the threads. Were PMs reported that were sent from one member to another to further a disagreement that started in a thread? Did we send PMs to tell someone to cool it before we shut a thread down? Is there some history you aren't aware of that could make things more complex that they appear on the surface? There are a lot of things to consider when making a decision, and it isn't always easy...