Even the wikipedia page tells us that repetitiveness is one of hallmarks of Asperger.
The question why, still unanswered, is much more tricky. It seems that, like it is with a language and many other traits, there is a genetic predisposition and environmental conditioning (training). It seems that autistic people has some genetically transmitted factors, which, if behavior patterns in early childhood is not corrected, would result in behavioral deviations, such as extreme shyness, inability to maintain an eye contact, sociophobia etc.
The famous "mind blindness", it seems, is an effect, a symptom, not the cause. Those children just didn't train themselves enough to recognize facial expression patterns properly because, perhaps, some inherited changes in the "social areas" of the brain which, for example, perform facial expression recognition.
Why are such areas supposedly exist? Because even newborns could distinguish calm and friendly face from angry, etc. Facial expressions is the most efficient way to read other people's emotions, along with other non-verbal bodily ques, such as posture and jerky movements. No one taught them to do it, so it is somehow hard-wired. Animal, of course, also read body-language, much better than we are.
Inability to read (or rather interpret) other people result in excessive anxiety, almost physical discomfort, and repetitiveness, as an effect, is probably an acquired habituation to deal with that anxiety.
I think "too many behavioral loops" is an elegant way of succinctly explaining a lot of the symptoms of autism, but there's more to it, and moreover, "too many behavioral loops" can describe other forms of cognitive dysfunction. Anxiety disorders like OCD come to mind.
Anyway "Mield [sic?] forms of autism, by the way, is when you have too many of such behavioral loops" is incorrect. I don't think that simply exhibiting the "behavioral loop" symptoms would be sufficient for a diagnosis at least.
I think you're close, but based on my layman's research (and my own experiences), the theory that in my opinion best explains the variety of symptoms (anxiety, meltdowns, sensory processing issues, mind blindness, repetitive behavior and obsessive thought, etc.) is the 'Intense World Theory'.
The basic idea is that people with autism (or at least a big 'subset' of what we now call autism) are born with heightened sensitivities (or 'differences', in some way) on a very fundamental level. Whatever the exact cause, the result is frequent (high-functioning) and sometimes constant ('full-blown', to use the proper term :P) overload.
Or to put it differently, from the outside it looks like autistics are trying to navigate a dark basement with dark shades, where perhaps the real situation is that they're trying to navigate this room with night-vision goggles. In both cases they keep bumping into things and are 'deficient' in a number of ways. However, in the first interpretation, the problem is that the bare bulb does not provide enough light when wearing shades, whereas in the second interpretation the autistic is blinded because the light overloads his night-vision goggles.
Obviously, which of these is true has effects on how to treat the problem, assuming it's always one or the other and assuming there's not a third option, of course.
There is growing support of this theory, and Temple Grandin touches on it in her book 'The Autistic Mind' (which I find refreshingly hard-sciencey in its approach. More emphasis on brain than on mind, so to speak).
That said, a common criticism is that Intense World Theory perhaps explains a bit too much. And it's relatively new and basically the opposite of many of the previous theories.
Despite this caveat, the reason why I strongly support the theory, even if it might ultimately be entirely or partly wrong, is that it fits much better with the self-reported experience of actual autists, both high-functioning and low-functioning (in the cases where they find a way to communicate). And actually listening to the experience of the person suffering from something strikes me as rather crucial when you start talking about causes.
One reason why I dismissed the possibility that I might be autistic is that I simply did not identify with the descriptions. It was only after the diagnosis that I realized that the symptoms were ridiculously applicable to myself; it was just the underlying explanation that seemed like the opposite of my own experience. It baffles me that problems making eye-contact (the symptom) is still very often said to be because of an inability to understand it, or something like that (the purported cause), when most autistics I know or read about self-describe the cause as being 'overstimulated' and simply not being able to maintain eye contact because it's all 'just too much'.
I can strongly recommend 'The Autistic Brain', by the way. It's very enlightening.
Attribution please.