Two major reasons: traditionally, stick people are just never drawn with such details and it gives me more options for when I have to decide what physical traits make a character recognizable. C3-PO, for example: if everyone had eyes, he’d be harder to identify.
Remember in Return of the Jedi, when Jobba’s feeding them to the sarlac and R2 has the lightsaber in a compartment in his dome? There is a theory that Luke got that idea from this scene. Also, since I probably didn’t draw it clearly, if you watch this part, there does appear to be something that resembles a lightsaber protruding from the hole.