You've answered your own question here. It's not so much about what precludes you from selling something digitally, as it is about what precludes that person from simply making copies and distributing them for the marginal compute cost plus some profit. The answer is copyright law, which has been steadily strengthened over the years in response to the lobbying of corporate copyright holders. In order to sell even one digital copy to another person, they'd have to buy the copyright from you. And why would you sell the copyright to them when you can leverage it to sell licenses instead?

Agreed that I should've said "there is no such thing as digital ownership in practice", at least for consumers.