Applications list only fills the Activities zone if screen resolution is FullHD

I have an external monitor with a resolution of 2560x1440 pixels, and I noticed that the Applications list doesn’t fill the Activities zone, as seen in this capture:

There is a black margin around the icons.

Instead, if I switch to the laptop’s screen, which is 1920x1080, the screen is filled with the icons, as expected:

Is this a bug, and it should fill the screen with more icons in my bigger screen, or is it a feature, keeping the number of icons to a minimum to avoid “overdriving” the user?

The number of icons is fixed as is the list of possible icon sizes. If the layout does not fit with one icon size, the next lower one is used.