People used to buy DVDs or blu-rays for $10-20. But of all the ones I have, there's probably only a handful that have been watched more than once.

That's what the renting system is built off. The fact that most people only watch a film once.

I couldn't care less about whether I own a copy of a movie. All I care is that I can watch it when I want to watch it. That's a different issue though, not one of disposable income, but of licensing and content availability.