Well, as Satoshi created the forum only Satoshi would know the answers to your questions. What and why Satoshi did or did not take in to consideration or what the reasons were for Satoshi using a particular forum back in 2011 is something we could all speculate about but would not have a definitive answer to. Maybe one of the admins would be able to provide some answers.
Recently I installed a forum for testing. I used phpbb on it but later I realised that it has a big demerit that the URL it gives does not contain the content of title of thread. I checked this forum and here also the issue is same. Was this not taken into consideration while choosing forum software ? Or does it not matter much? Are there some special benefits of SMF over other popular forum softwares like xenforo or vbulletin?