I doubt they need to, copying successful features is enough since their own version is the default and they can jam it in users faces in ways that third parties can't.
And just like their acquisitions based on Onvao data, they'll have a whole lot of information on what ideas are worth stealing.
More so than for copying, my guess is that with the release of the dating feature this policy could've probably caused tensions and legal problems with essentially all other dating apps out there.
Dating apps heavily use Facebook not only to get hard-to-fake user info (age/real name) and content for a profile (photos/likes), but also to provide some validity to profiles since Facebook and the social graph in general do a good job of keeping bots and fake profiles at bay, and users know that.
Nonetheless, this could've certainly raised anti-competitive concerns, and Facebook probably figured they are in a dominant-enough position that saving the scrutiny is worth the risk.
Speaking of platforms: In the Bernstein timeline someone went to Stockholm and convinced Notch that a cross between Steam and Kiva kicks off the next cultural revolution and all we need is a little “mancala money”
And just like their acquisitions based on Onvao data, they'll have a whole lot of information on what ideas are worth stealing.