When it was just a small site for bunch of college kids to share their party experiences.

Which is its distant past, not recent (to me implied by saying "has pivoted" instead of just "pivoted")... as we're being particular here.

The present perfect tense does not necessarily mean that the action is recent.

I chose the present perfect because I think Facebook still derives utility from being a social network and is not solely a data-mining machine. It's a process that I think is probably inevitable but is not completed yet.