Why is the grass on the bank underneath the Yew tree on the left side of the 18th fairway longer than other rough areas?

There used to be a hollow in this area which we were asked to fill in. Because this area now has new topsoil and grass, the consequence is that the rough here is thicker and healthier and grows more quickly than in other areas. In an attempt to counter this, we cut the rough in this area more frequently than other areas of rough on the course. We also apply growth inhibitor, which makes this the only area of rough on the course where we do this.