system
Given the following post, respond as if you're commenting on Reddit:
human
[Robot/Empire/Foundation] In over 20,000 years of Galactic History, Spacer tech of robots and life extension never re-appeared across Galactic culture. Why?

There was a huge culture clash between the the first interstellar culture, the Spacers, which started out in the 21st century, and the Settlers which came 1500 years later.  Spacers viewed Settlers as declasse and vulgar,  and Settlers viewed the Spacers, genetically engineered to live over 400 years, as effete and decadent, hopelessly dependent on robots, and had a great dislike of Spacer technology.  

Eventually the Settlers won out and the Spacer populations either died out or were absorbed into Settler populations.  But the Settler wave of immigration started around 3500 AD and the Galactic Empire was founded around 12000 AD.  By that time, the conflict between the Spacers and Settlers was ancient history and the Spacers were all long gone.  The Galactic Empire lasted 12000 years before the Foundation, and by that time even the existence of Earth was a lost, forgotten memory.  During this time, it was explicitly stated that not even the Emperor of the Galaxy had access to life extension.  

So in over 20,000 years of time and technological advancement, none of the tens of thousands of worlds of the Galaxy, during pre-Empire, Empire, or Foundation times,  ever re-introduced either robotics or life extension?  How did this not happen?
gpt
R. Daneel Olivaw is why.  
Seeing what life extension technology did to the Spacers, Daneel was convinced it was in humanity's best interest that such technology not be used.  
From there he is compelled by the Zeroth Law to manipulate human affairs such that the technology never gets redeveloped.