So what happened? As heralds started conflict checking against more and more mundane armory, it became more and more difficult to pass simple, "core-style" period armory. Heralds at the consultation tables began to develop work-arounds such as adding a peripheral charge (e.g. a bordure or a chief) to clear conflicts. Someone noticed that the more complex armory was getting passed, and someone else noticed that even more complex heraldry could be justified by citing Tudor styles, which were at times ridiculously complex. It became common to see four or more types of charge on a shield. The rule of thumb (total complexity count of 8) was developed to keep things from getting too complex, but still allowed for a great number of dreadful submissions to be passed.
A little bit of knowledge thus did a great deal of harm. Non-heralds, seeing the complex armory borne by their compatriots, designed their own heraldry assuming that such was an acceptable norm. They came to the tables with depictions of their entire life story on shields, and the heralds held their noses and passed them. Many new heralds accepted this complex style as well, and as the old generation took a backseat, the new generation actively encouraged awful designs. Now, it's "common knowledge" that you can't have a single charge on a plain field, because they're all taken by now. 2/3 of arms registered in the Society would never have been plausible before the Renaissance, but the submitters don't know this and the CoA don't seem to care.
I've tried to fight it with my own submitters, when I can, but I can't see much that I can do at this point, particularly when new research into the anomolies of period heraldry have revealed quarternary charges, banana crescents and other hindrances to identifiability across a field. And I've come to learn that if you tell someone in the SCA that something was done once, by accident, in period, it becomes the new big thing, everyone wants to do it, and all of a sudden we're wearing shoes on our hands because "it's the way it's always been done."
How do we turn this ship around?