What was the cause for the current overwhelming popularity in the brighter, more acidic coffees? Almost every coffee shop I go to serves up quite acidic and bright coffees. It seems that this is where modern coffee is and is not necessarily a bizarre phenomenon in itself but in particular the world of espresso it has veered quite far away from the traditional Italian style.

In fact it seems we've veered so far towards acidity and people have actually called the Italian style of espresso as 'over-roasted' which I believe to be untrue. I do enjoy a somewhat more acidic coffee when I am searching for a fruitier cup but I do not understand the current stigma against even the slightest darker roast.

So what caused this tip in the scales that prompted the surge in popularity in brighter and more acidic coffees and seeing even the slightest darker roast as being over-roasted?
I think there are a number of factors influencing the current situation.


The rise of micro/small and home roasters.  This allows people access to fresher coffee.  The acidic and bright notes in coffees tend to fade quicker than roast notes.  Meaning these bright notes are more readily available to the consumer.
Changes in coffee processing.  Different process methods favor different flavor profiles.  Dry Process (the oldest) favors less bright and more bodied flavors.  Newer processing methods enhance bright flavor profiles.
The rise and market dominance of large chain roasters.  These companies tend to roast dark because it is easier to hit a consistent flavor profile which lasts longer (important for shipping), but it sacrifices the origin flavors which are varied greatly and available.  They have given dark roasts a more McDonald's character among consumers (consistent, but not high quality). 


This is not to say that dark roasts are bad.  But they have partially been given a bad rep by large chains who are using them to maximize profit, and not flavor.  Home and microroasters now also have unprecedented access to a HUGE variety of beans that years back would have been out of reach.  This means that companies can cheaply distribute very high quality beans with extraordinary flavor profiles when roasted at a lighter level.