"Mr Data, Warp Factor 10."

    We have here a chicken and egg kind of question.  Did technology create the ever increasing speed with which modes change; or did the increase in changes help drag technology forward?

    The answer is of course, both.

    For the first 1300 years post BC, styles were pretty much in stasis.  First of all because so little trade to and fro was going on, and because the level of education was so close to zero, unless one were Catholic clergy.  Even some sovereigns couldn't read or write.  But along with the end of the Crusades, came an increase and interest in things outside one's own little sphere, and the splendid things that had been brought back as spoils, began to inform design in textiles, in particular.
    Now, of course all fabrics had to be hand spun, and hand loomed, and the jacquard loom was a long way off; so complex patterns of this sort were even more time consuming to create since the weaver had to keep track, thread pass by thread pass, of where they were in the design.  A single meter of such an involved textile would have taken days to make.
    As trade between nations increased, most especially with the East, and with a rise in information technology through the printing press in 1450, things began to move at a faster pace.  From about the mid 1400's on we see an ascending curve in the speed and universality of style changes.

In the early 1400s, things looked like this.

    By the mid 1500s they looked like this.

And by 1600, they had morphed into this.

    So in a scant 200 years the ossification of the prior millennium and a third was washed away.  We went from primarily loose, unstructured garments that owed much to classical drapery, to clothes that were not only complex, but rigidly structured and contained.  This rigidity of structure mirrored the structure of society which was daily becoming more carefully codified and set about with rules and regulations.  As well, the increase in complexity of structure gave ample opportunity for displays of significant wealth, through the use of expensive and literally rare textiles, and carefully worked embellishments.
    Now, take a look at what just 50 years brought.

    From here on changes continued to accelerate, but we have begun to see here with these images above, the beginnings of a pendulum swing from tight to loose, overtly sexy, to constrained.  In the mid 1600's the restraints of the reformation loosened, and so did apparel.  The clothes above are deliberately sexy and enticing, not so their predecessors of only 50 years time.
    The 1700's took us through another phase of constraints and releases, but as we got further into the century, the ever growing number of social rules of conduct began to stiffen, quite literally, the shape and execution of clothes.

    Once we get to the 1800s, with the beginnings of ready to wear, the increase in textile manufacture technology, and the growth of trade and exploration, we are really gathering speed.  Throughout the 1800s, changes in style and silhouette are occurring decade by decade, as opposed to the more generational changes previously. 
    And by the 20th century, shipping by rail, boat, and plane added to the vast growth of manufactured goods, means that change can happen with even greater rapidity.  Through the 20th, styles lasted, with a few exceptions, no more than 5 years before being supplanted.  And now, in the 21st, prevailing modes barely make it through a year.  Things are on trend for months, sometimes even only weeks.
    This rapid fire change is helped along by computer technologies that allow a designer on one continent to design a garment in C-Cad, send the file to India to be made up, where they will shoot video of a model wearing it so the designer can make changes, and have finished designs patterned and ready to go into production in a matter of a few days.

Marry body scanning technology to computerized pattern making and robotics, and you get to a point where a client could walk into a store, pick a design and a fabric, and have a custom made and fitted garment delivered the next day.

Whew, I'm dizzy now.