Counterpoint, the cost of "owning" offline games is not zero and their lifetime is not infinite.
I have a stack of old games on CD (or older) and getting them to run on anything is a massive pain in the neck. (In fact, for nearly all that I care about I also have bought a Steam license in addition).
Ultimately, everything comes down to user experience. We can pat ourselves on the back for buying something forever, but experiences and the media they are stored on are both transitory.