In your area, I would guess that it is a result from the hurricane(s).

Here, they looked great, very dense, thick foliage, until the cold spell last week(26F), which froze most of the leaves on the plants. Even after several light frosts, it still had great looking foliage, but being cold hardy to only about 30F, the lower temps for an extended period of time, did the leaves in.

Last Winter, temps never got down below 30F, and the one I had in a pot outside, remained thick and bushy.

Other reasons for thinning could be a lack of water at some point, too much heat, wrong soil type, leaf eaters, or any combination of these.

Kt