Maybe? The thing is that the incentives don't really align to make this a real priority of theirs and they've been pretty clear that shipping physical DVDs is not their long-term business model. So long as a lot of people don't start canceling their DVD service because of unavailable disks, they don't have real reason to replenish.

Of course, given that they pretty much put every other rental place out of business, your only choice in a lot of cases is just to buy a disk if you want to watch something that isn't available streaming.