I can’t speak for why it’s not included in the diagrams, but my guess is that it just serves to confuse things. The treatment for ground wire connections is the same for smart switches as it is for dumb switches. To be honest, if you have to ask, you might want to consult with an electrician to insure that your installations are properly wired.
That being said, the switch needs to be grounded. This depends on the type of wiring used, but with Romex wire that contains insulated conductors and a bare ground, you should pigtail a bare ground wire to the bare wire bundle in the box and connect it to the green screw connection on the switch. To obtain a bare pigtail, cut a length of Romex and pull the bare conductor from it.
That ground is always connected to the green screw, period. It doesn’t vary, so it doesn’t serve any purpose to include in the drawings.