Bunkerchan was well known for its persistent technical problems for years which lead the site to frequent crashes and outages especially during periods of high volume of posts. These problems couldn't be fixed that quickly, sometimes for DAYS, because the site owner refused to allow the staff to have server access, and also didn't fix the problems quickly on his own either. Also he rubbed people the wrong way by generally being a petty smug asshole.
The moderators started to make their own website as a plan of last resort. Once he found out about this he got mad and decided to kick out all the mods that participated in this endeavor. The moderators refused to allow this so the site owner pulled a 'Reagan breaking the traffic controllers union' move and fired them all. They ended up finishing this site, staying here and eventually everyone migrated over.
Also at some point a rogue mod who had mod status on both sites ended up deleting a bunch of posts over there. There was only one mod who remained loyal to the old site owner and after the split, the site owner got depressed because everyone left so he gave ownership of the site to that last mod guy who is the new owner of bunkerchan.net
Now most people have migrated here and the old site is filled with right wing crossposters, spammers, etc.
Maybe its just my biased opinion but the main reason for the fall of bunkerchan was Space_'s egotism and arrogance, not by simply refusing his staff's demands, but also being very cryptic and condescending about the whole thing too, actively mocking and antagonizing them by telling them "its my way or the highway, if you don't like it, leave". Then once they did and he discovered that running the site is actually work, he fucked off and handed it over to someone else.