Agreed. I don't read many books, but I asked my wife about the last 3 ebooks she'd read. One of the three was already a free book due to Amazon prime and was also included in Kindle Unlimited. The other two weren't available as part of Kindle Unlimited.

So comparing Kindle Unlimited to Netflix's online streaming is actually a pretty accurate correlation. It's currently comprised of second-tier (or lower) books that aren't likely to yield the same profits as new and currently popular titles, so they're used as filler for this service.