It is because certain users are digging through years of old posts looking for things to report as a form of censorship and gas-lighting, and the mods are either complicit or mindlessly rewarding this abuse of the reporting system by giving them the results they are after.
The mods are definitely complicit especially given they then send follow up messages to taunt and gloat they have done it (as reported by me elsewhere).
Threads that are nuked don't show up as "A reply of yours..." so we may never know how many of our old posts are quietly being deleted.
An example of which - user Neopotism
https://bpip.org/profile.aspx?p=Neopotism was Nuked in the last week, all three of their posts were merited.
I wonder if @theymos knows his staff are freely deleting posts and even Nuking them simply because of what they have said and about who.