Campbell
Relaxed Intensity
It's largely about the design space assigned to the different subsystems. Powers represent abilities that require active action and due to their costs (both in terms of the action economy and daily and encounter limitations) they get more impressive effects. Feats, on the other hand are used to represent passive abilities so their effects tend to have less oomph. Whereas in 3e feats tended to occupy both design spaces for more martially inclined characters.