If you mean clone the features over to Facebook.... It's because Facebook is unpopular with teens. That's a demographic Facebook has increasingly lost as it pertains to usage (they still sign-up, because of the vague pressure that everyone must have an account). If it weren't for Instagram, they'd be in deep shit with people under ~25 and very susceptible to being replaced or having their monopoly fractured (the 16-25 group would seed competitors, one of which would eventually kill Facebook starting from that base and progressing up).

It seems to me that Facebook has the age data and could have just targeted those age groups exclusively with the feature, and hidden it from the uncool age groups. Maybe they tried it and it didn't get any traction and that's why they did the purchase.

Like when Facebook made their "Poke" app to compete with Snapchat and it failed miserably?

Facebook is like a telephone directory to teens. You're in it, but you don't care for it. For want of a better term, it just isn't cool. Of course it isn't, your parents are on there.