Lxqt-config-globalkeyshortcuts and lxqt-config-brightness

At lxqt-config-globalkeyshortcuts to adjust brightness by default assigned
lxqt-config-brightness -d
lxqt-config-brightness -i

It don’t work. Although lxqt-config-brightness works fine from QTerminal.

I change lxqt-config-brightness to xbacklight (inc/dec). And keys begin work.

The problem seems to be solved, but I’m just wondering why lxqt-config-globalkeyshortcuts don’t bind keys to lxqt-config-brightness and sucsessfully bind to xbacklight?