This board seems to shift every few years.
When I first arrived, the build threads were pretty direct. OP would ask for opinions on specific things, people would give their 2 cents, then OP would either take their advice or not.
There wasn't much in the build threads that wasn't build related.
Then it shifted to a lot of banter in the build threads; 30 page threads with the majority of pages not containing any actual build progress or information.
Then it shifted to people giving their two cents, not being happy that OP doesn't agree with them and continuing to argue or pile on for five pages.
Here is an example of a thread that if posted a month ago would have been turned into a 30 page debate:
http://forum.arcadecontrols.com/index.php/topic,81520.0.htmlPeople give their opinion and moved on. Strange times.
LOL at the Egoist. Not calling him out, but I found one build on over a half dozen sites.
The person posting it did not have any other posts on any of them except to post pics of their project and respond to the praise.
After a few weeks, they were never heard from again.

I'll add:
The Conversationalist (not to be confused with the Squatter)
The build thread is 80% unrelated banter. The cab is getting built, but any useful info is buried in pages and pages of unrelated chatter that nobody wants to dig through.
Sometimes it isn't even the OP that is filling pages with unrelated stuff.
As far as why people are dropping completed build pics and moving on, only the people who are doing it can say why.