Simply because they like it, want it, and can afford it.
OK. Obviously, there are still some people buying prints from not insanely famous photographers or hiring photographers to shoot special occasions, catalogues, etc... I am not disputing that.
But there are less and less of them and more and more content to be had for free. Plenty of it is very good. And it is not only photography, music sees the same evolution. So, enormous amount of content is to be had for free and I think that is what the citation refers to.
On the opposite spectrum, you have large amounts of public being prepared to pay, as long as a celebrity is involved. Probably, they are not really paying for the "content", but rather for the privilege of being a fan of the celebrity (think about brands "endorsed" by a celebrity", for example in clothing).
I have a feeling that all this is indeed a worrying trend.