Steam was by no means the first form of DRM

While there was a game that had online authentication before Steam, Steam popularized it to make it industry standard.

Copy protection is very different than online authentication that restricts your ownership rights.

. If you bought a CD or floppy disks in a store, you were buying a license to use the code on the disks, but you were explicitly denied the rights to resell

Absolutely untrue! You were denied the right to copy the software. If you bought a CD, you absolutely had the right to resell it.