My guess is that it's to keep it center-aligned with the main part of the keyboard. The Librem 15 has a built-in numpad on the right, which pushes the letter and number keys over to the left.
Personally I'd have them just ditch the numpad entirely and center everything, the way they do on the Librem 13. USB numpads are cheap and widely available for those who need them, and typing on an off-center keyboard feels weird.
Personally I'd have them just ditch the numpad entirely and center everything, the way they do on the Librem 13. USB numpads are cheap and widely available for those who need them, and typing on an off-center keyboard feels weird.