Quoted:
According to Popular Science, the first few times the M-16 was issued for combat (Vietnam), it did not come with cleaning supplies. Complications further arose when bullet manufacturers at the time started using a new type of gunpowder that left "gobs of calcium carbonate in the gas tube". So then they started to issue cleaning kits. Later on, the military chose to use a chrome-lined barrel to make it easier to clean.
Just from reading this article, it would seem like the majority of Col. Hackworth's complaint seems to stem from what happened from 1965-1973.
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Sometime, if you ever get the chance, I would suggest reading "The Black Rifle". It has far more detail on the developmental/deployment history of the AR than most regular gun nuts would want to read but they do go over that whole deal in pretty good detail.
The two things that happened to create a bad introduction were...
1. It got promoted as so hi-tech that you didn't even have to clean it.
2. It got issued with much dirtier ammo than originally tested with.
Those two really culmenated, in a bad way. :(
There were other problems but 40 years of development has certainly led to minimizing (or ending) them.