Or they want off the upgrade treadmill. Microsoft's traditional model only worked if customers needed to routinely update to the latest version, and so pay for it - but is that still true? Look how many years it took them to drive customers off of XP, and Windows Seven is still in common usage. Office is the same: For a lot of customers, Office 2000 would still do everything they need, and Office 2013 is good enough for almost all.
In software, if you make a good-enough product, you deprive yourself of the chance to sell later versions. People won't pay to move away from what works without a very good reason.