Used physical copies degrade and are an objectively inferior offering to new copies.
Digital copies don't degrade unless artificially made to do so. The copies can be traded for infinity without ever degrading or lessening in value. Which essentially mean that with time the demand for any game would be vastly outnumbered by the supply of cheap "used" copies that never ever degrade.
It would be very hurtful to indies since they will be the first ones to have their games dumped on the market, even if they're good.
A major issue with this is that digital goods do not degrade or deteriorate, unless built-in.
For indie games, a free "used" digital goods market would mean the end of sales for that indie game.
How many gamers would not sell off their Subnautica or Super Meat Boy in a heartbeat just to spend that money on Cyberpunk 2077? Many I guess, in the thousands even.
So very shortly the supply of "used" copies of a game would VASTLY outnumber the demand for that game.
Thus effectively ending the sales period for that game, probably forever. No reason whatsoever to buy a "new" copy of a digital good unless it uses some additional DRM locks and microtransactions.
Now why this problem isn't as prevalent with physical copies is that:
A) It's actually not legal (in many jurisdictions, at least the ones with copyright lobbies, of which there is no shortage of in the EU) to make copies of the discs for any other purpose but personal backups.
B) All discs deteriorate and degrade with time and they can't be circulated forever due to point A.
If an open market of "used" digital goods becomes the norm then that could spell the end for many smaller studios as we know it.
Or it just makes a Streaming future even more inevitable, or Steam will invent some clever thing to circumvent this whole thing.
Maybe instead of buying games you simply buy "tickets", I leave this up to the lawyers to figure out.