The cynical answer is that bookface is turning a blind eye to content theft because they need the eyeballs on videos, regardless of their provenance. It (theoretically) helps metrics and allows them to woo advertising money.

There is no proof of this, I'm sure a ContentID like system is prioritized or even is implemented. Ultimately if you're a legitimate content producer, having a system like this in place would only encourage you to use the platform and it would have a net benefit to usage overall.