Xev Bellringer: The Brunnen-G discovered eternal life, but they all died. You were the only one to survive.
Kai: I did not survive.
Kai: You might consider abandoning Lyekka on this planet.
Stanley Tweedle: But I like her... when she's not hungry anyway.
Kai: The dead do not poo.
790: You're not going anywhere until I deal with the sizzle... in my pizzle.
790: 29 hours of necrophilia-filled fun.
Answer: From what I'm seeing, the answer seems simple. The robotic heads allow the control of the body they need. However, no mater how advanced you make a robot's body, it will never quite be as flexible and versatile in it's movements and actions as a flesh and blood human body can be in most cases. And if they do put the effort into creating a robotic body with the capabilities they need, and be durable enough to last... it would cost a lot of money. The Cluster has a large influx of constant prisoners that they use for feeding the Lexx and other needs, so human bodies are easy to come by and in vast quantities. Them simply producing robotic heads with the ability to interface with the human nervous system and placing them on the decapitated bodies of expendable prisoners is a hell of a lot more cost effective and easier to do with the technology they have. It's just a cheaper, more effective option for them to have thousands fo 790 Units in production and use without the cost of manufacturing a fully functional and durable robotic body for them.
Quantom X ★