For the consumer, DRM simply makes it a product not worth investing in, because you don't own it, can't promote it to others, can't recoup any cost of, or donate to the library. As things change beyond your control (tech changes, company goes out of business, service is stopped), you lose it, despite having paid for it, without recompense.
For the producer, DRM simply makes it a product not competitive with others, costlier, with diminished promotion/word of mouth advertising (free), and without resale value.
For producers, DRM free products that are copied have been shown time and again to bring in more income.
I have a friend who is an author, she doesn't understand this either. Marketers do. This is a reason content producers need marketers, to increase their sales.
The ones who want DRM are the ones leeching off content producers, the publishers. They try to lock down content under their own purview, via exclusive contracts with content producers, and any other resource at their disposal. They claim their investment in infrastructure/resources warrants it. Content producers have to make their own decisions accordingly.
Once you understand people want to pay for things they value, and those who don't are not your market anyway, it all becomes much easier to accept/understand.