What an interesting discussion! Although I'm not really in a position to judge the trends on this forum since I've only been here for a short time (though I have read the blog daily since about 3ish years ago), here are my two cents on the matter.
1. I agree completely with Claire about sometimes using more accessories or layers to cover an outfit flaw. I think it can also be done to disguise the fact that each piece isn't the best quality. As a college student, I have done this more times than I can count. If, for example, I know that my blouse is slightly faded or a little worn out, I am much more likely to cover it up with a cardigan or necklace. In a minimal outfit, there are fewer pieces, thus making the necessity for each piece to be of a better quality in order to project a polished outfit. I think this works with fit too. I have a few layering pieces that I would never wear on their own because the fit just isn't good enough. I also have a few pieces that fit me so well that I can't bear to cover them up with any accessories.
2. I also think that there could be a learning curve with fashion. I have experienced this myself. When I first started trying to dress myself better, I dressed extremely minimally because I had so few pieces that actually deserved to be in my closet. As I slowly grow to learn more about my style and what works best for me, I'm starting to get more maximal because it's just so fun! However, I think that once I figure out exactly what works for me (and have the money to buy better quality pieces), I will probably become more minimal again.
Of course, I'm not saying that a maximal outfit is a bad thing by any means--I love a good maximal outfit, but I think the two reasons above could possibly be reasons why some people could start to lean towards a more minimal style.
Also, Amy, in response to your comment regarding age groups, I think you do have a point. I guess I'm a minority here (I'm 19), and I think that teenagers/young adults do tend to dress more maximally.
Does this make sense to anyone or am I batting out of left field here?