Any idea what it is? Looks a bit like a Rhododendrum some of which do grow into almost tree like shrubs with not much lower growth. Top looks healthy, perhaps you could experiment and cut back a couple or three of the outer branches and see if it shoots out lower down.

Yes it would help if we could identify the shrub as some will shoot from lower down if cut back and others are more reluctant. Can you add a nice clear photo of a one of the healthy shoots? Some shrubs do behave like this and a good way of dealing with it is to plant something smaller and bushy in front of it to hide the bare stems.