Pvp combo action buttons work well in pvp because all the classes are drastically stripped down to a very basic level.
Classes are far more complex in pve. Not only would the combo action button dramatically reduce the amount of skill and knowledge needed to play some classes, they would be laughably simple compared to others who cannot benefit from this feature. This would cause severe imbalance. Nevermind how freaking dull it would be to spam one button so much.
There are other ways of reducing skill bloat that can benefit all classes instead of using a system that clearly favours a certain type of class and is completely irrelevant to others.