LifeinAsia - 5:19 pm on Mar 5, 2013 (gmt 0)
BeeDeeDubbleU's answer was my first thought... I can certainli imagine some of them being upset at other people "giving it away" and taking away their market share. :)
But if you think about it a little differently (adult movies), it's actually a serious answer. With many people posting their homemade videos (with or without the permission of all parties involved), people don't need to pay to watch the "pros" (and given the number of free sites, people don't even have to pay for that either).
And jecasc's post sparked a more serious answer: writing. Many "amateur" writers use non-traditional publishing methods (blogs, e-books, self-publishing) that could make "real" writers (not to mention their publishers) cringe.