Executive Meddling: According to Wikipedia, the syndicate requested that Meddick phase out Robotman from the comic, because of marketing difficulties with Robotman. He did so with an epic storyline of Robotman being abducted by aliens, fighting Captain Kirk for his freedom, and meeting and eventually settling down with a Robot Girl on another planet.
Merchandise-Driven: Robotman was created by the syndicate and then giving it to Jim Meddick hoping it would be part of a line of merchandise. The plan failed almost immediately and the strip became the only surviving aspect of this scheme. If you look at the very early strips, Robotman looked more toyetic (for what it's worth).