Warren Smith wrote this great article called God, Mammon, and the "Worship Wars". I strongly recommend reading it. Essentially, he briefly outlines how the rise of the "worship wars" coincides perfectly with the establishment of CCLI (Christian Copyright Licensing International). He also points to the fact that this organization brings in approximately $40- to $50-million per year to copyright holders. One reason why you might be more likely to hear a modern worship song over a classic hymn? The aggressiveness of marketing connected with the multi-million dollar "Praise and Worship" industry.
Be sure to read Bill's blog on this article where I was first introduced to it. He has a lot more thoughtful things to say.