I think sales are bad because the buzz around Windows 8 has been fairly negative. The tech blogs and news sites have all latched on to the same message - that change is bad. It's fairly obvious to pick out the new UI, declare that foisting it on desktop machines is a bad thing, and then shout about it as loudly as possible, and that's exactly what they've done.
The reality is far less sensationalist, but enough mud has been thrown that some of it has stuck, and it will take time to undo that damage.
Microsoft could simply wait for the market to sort itself out -even Windows XP didn't get off to a great start for the first year or two- but I hope they'll go ahead and make some big improvements over time to show they are prepared to invest in Windows 8's success in the long term, rather than just focus on Windows 9.
Time will tell, but speaking personally, I like Windows 8 (of course I do - I bought a Surface!).