The "availability window" is manufactured scarcity. Those tapes were physical objects that they couldn't recall once they left the building, but with digital goods they can decide how much of which title to make available in order to manipulate the demand curve.
That's the logic for high-demand titles. The reasoning for not making all the junk available at a fixed cost is the flip side: if users had a giant library of good-but-not-hit content, they'd be less likely to chase around their HBO or Netflix or whatever licenses.
That's the logic for high-demand titles. The reasoning for not making all the junk available at a fixed cost is the flip side: if users had a giant library of good-but-not-hit content, they'd be less likely to chase around their HBO or Netflix or whatever licenses.