What I mean to convey by "well defined" is that even though the problem space of self driving cars is enormous, the success criteria of teaching a car to self drive is probably going to look pretty similar in 10 years to what it looks like now.
Bots on the other hand changes constantly - what is the definition of an abusive bot? What is the definition of spam? The adversaries on Twitter adapt not only their tactics but also their goals.
They problem is so ill defined that it sometimes has to be modeled as random events instead of a deterministic physical process.