With subscription based Creative Cloud Adobe gets to decide what updates are enough.
With old CS products you, the user, get to decide whether new features are progress enough FOR YOU.
With new CC you don't have that power to impact and show Adobe whether you're impressed with new offerings or not.
Last, you are more forced to buy new hardware since you can't keep using older CC software version forever since at some point in time Adobe won't let you run certain CC version anymore.
Lets say CC version 3.0 doesn't support MacBook Pro (2012 model) with Mountain Lion anymore, but you don't want to buy new computer just because of CC 3.0 because all your other computing needs are still covered AND you really don't find new features in CC 3.0 useful TO YOU. In this case you can only keep on using old CC 2 until Adobe lets you (I've hear old version are let to be run for one year - that's a lot less than forever).
With old CS you have the power to not pay and show your opinion on new updates (money talks!). With new CC you have not.