Speaking purely in the realm of Law, and what arguments will get past a court, "buying" a digitally distributed work does not confer any ownership. At the bare minimum, what is actually being purchased when you buy a digitally distributed work is a combination of a license and a service. They transmit the work to you, and you have a license to copy that transmission and store it indefinitely, for your own use. There is no "that" being sold, you are making all the copies yourself, so you need permission to make those copies. And permission cannot be resold.
In the law, a "license" is just permission from a copyright holder to do something. There are no standard terms like there is with a "sale", because licenses are usually tied to a contract[0]. And contracts can have really arbitrary provisions[3]. For example, fair use says you don't need permission from a copyright holder in order to review a game. But if that game is only available digitally, the copyright owner solely dictates the terms upon which the game is sold, through contracts and licensing. And that contract could absolutely just say "you agree not to review the game in exchange for permission to copy the game to your hard drive and RAM[4]", in which case there is no fair use anymore. In fact, Oracle already did this[1].
The law has no counter to this because, for the vast majority of copyright case law history, nobody needed permission to purchase a physical copy of a creative work[5]. Physical media has very well established consumer rights that were codified back when copyright law wasn't nearly as blatant a power grab. Digital is very recent, and copyright law has gotten significantly stricter. It's often said that "the law needs to catch up to technology", but that usually gets said in the context of "I thought of this cool little excuse to not get permission[2] but the court won't agree". Where technology really outflanks the law is in inventing new ways to strip consumers of their rights, by turning things that didn't need permission into things that now do.
[0] US law only. In other countries licenses are treated as separate from contracts, but this is mainly something plaintiff lawyers have to remember when drafting complaints, since "doing something without permission" is copyright infringement but "getting permission, but not fulfilling your end of the bargain" is breach of contract here.
[1] https://en.wikipedia.org/wiki/David_DeWitt#DeWitt_Clause
[2] Which will never be granted, mind
[3] The only real restriction on contracts being that you can't literally sell yourself into chattel slavery. BTW, in unrelated news, never upload your brain into a computer if you happen to like the 13th Amendment.
[4] DON'T GET ME STARTED ON MAI SYSTEMS CORP VS PEAK COMPUTER INC
[5] Thomas Edison tried.