Why: Dr. Zoidberg says "ROW-but," and so does Zack's dad.
Answer: Pronunciations are both ˈrō-ˌbät and ˈrō-ˌbət, but the audio only sounds like regular "row-bot." I'm just saying.
Source: Merriam Webster
The More You Know: This is what MW offers for etymology:
Czech, from robota compulsory labor; akin to Old High German arabeit trouble, Latin orbus orphaned — more at orphan