I've bought a number of media second hand to make sure I own them, and it's remarkable how there just is no way to pay any original producer for things in a lot of cases. I can download a movie easily, but there's no way for me to pay anyone for having done so - meanwhile if I buy a physical copy of that movie from someone else...the creator doesn't make any money from me at all, but it's all completely legal.
That's assuming second hand prices below the original price. Inflated prices for rare works (which could be easily republished as digital media by the creators) are a different story.
It's just, they don't even want to share the tiny bit of commission, or risk that you explore different content on these neutral platforms.
Some of my favourite local comedians sell all their stuff on Vimeo. Its like USD 3 for a show, and they have apps on most common devices.
Naturally I consider those more rentals than purchases that can be removed at any point in time, but thats a different topic
While distribution is basically free (pirates do it at a very low cost), having a payment system set up for these "unusual" purchases costs more than the revenue is worth.