> I seem to recall trademark troubles with Oracle, which led to everyone forking and starting Jenkins.
Well, you have a keyword in there, "everyone". All but 1 major contributor (not even the main contributor and definitely not the project architect and lead) disagreed with their decision.
Oracle persisted with the help of that major contributor - an Oracle employee, BTW - and while Jenkins was being created, they did not want to contribute and instead tried to create a competing effort over at the Eclipse Foundation.
Jenkins was receiving 95% of the contributions because, as you said, "everyone" was helping out, while Hudson was slowly dying on the vine at the Eclipse Foundation, and Oracle was putting out cheerful release announcements for it <<for years>> even though anyone who checked the commit logs could clearly see that Hudson was dying.
Oracle kept pushing with Hudson internally for quite a few years but even they gave up and buried Hudson a while ago.
Similar story with OpenOffice. They <<really, really>> wanted control so they forced everyone else to force through their actions and OpenOffice basically had the same face, Apache Foundation, death. Though OpenOffice is more of a zombie these days, I don't think it's been shut down completely like Hudson.