Second hand items are often

* Lower quality, as they've been used * Lack consumer protections

The first just doesn't apply to digital goods and the second is much more minor (not expecting technical faults to become apparent after a while owning a digital item).

Selling physical goods also has a reasonable time commitment to it, you have to physically move things - there's friction. Digital goods could be sold between regular people near instantaneously. Buying a DVD and selling it after watching is do-able but still some work. Buying a film second hand the moment I press play and selling it on a market straight away after I stop watching seems trivial. I know this is ~rental, but theoretically users only need to buy in total enough copies for the concurrent number of watchers. A big enough market and this could impact how things are released, a "watch anytime" vs a "you really need to be up to date (e.g. sports)" would make a vast difference in total required copies floating around.

The resale value impacts the price you can sell at too. If a customer knows they can easily sell an item for 80% of what they bought it for, they're likely to be willing to pay more for it. However the customer also takes on more risk.

It feels like such a small change, but I can see it making a very large difference.