First sale doctrine (in the US) said the buyer owned the physical copy and could resell or do what they wanted with that single copy.^
Obviously, that isn't portable to a zero-copy-cost digital realm.
However, the "buyers never actually own anything digital" modern reality is vastly different than the historical norm, in favor of publishers and platforms.
What was missed was the conversation around what baseline we should establish around digital ownership.
We've nibbled around the edges (you have a right to decrypt something you've purchased, in some cases), but we never clarified it sufficiently.
And without clarity, buyers only get whatever rights publishers/platforms decide to grant them.
IMHO, we'd be better served by establishing a clear floor of digital ownership rights, that no publisher or platform had the legal right to remove or obstruct.
That's how we did it previously, and it worked well...
^ There were some exclusions around mass/public broadcasting, but those were pretty limited.