Why do members do that? I think everyone likes it when have a high rank
At what cost ? If you mentioned your contact details on a thread by mistake, will you leave it undeleted even after realizing the mistake just for the rank on bitcointalk ?
the details you specified will remain archived. so we won't lose a single post that we can find even if it's been deleted.
this is normal and a lot of sold accounts do. and also the old members who cleaned up their posts that looked bad in the past to make them look tidier. like accounts starting in threads with POA and bounty campaign reports. then they cleaned it up and started being active on the forum again with better progress.