AMD, for all the work they put into their products, trying to stay alive... neglects the simplest of things that make people say they'll never buy AMD again. The SMBus driver is an example. I've never actually seen an AMD chipset driver installer install that one driver. It's always up to the frustrated owner to figure out what's wrong with their computer and then what to do about it. The driver may be there in plain sight, but the novice user that is about to build their first system hasn't a clue that the thing exist. They clicked the button to install drivers and then they all didn't get installed. The SMBus didn't used to be such a problem, it was rare, but these newer boards all have it but the supplied CD/DVD that is shipped with these boards won't automatically install the thing.
Why did yours get uninstalled? Tough question, almost as tough as 'Will AMD ever learn, before it is too late'?