The recently announced acq. of Lynda seems to indicate LinkedIn trying to penetrate other markets. If the revenue source from the main product is waning, they could diversify revenue streams or purchase a value-add company making their overall offering more competitive.

Maybe they are trying to reposition as a credentialing institution, where people can network, build skills, and manage their professional calendars.

I am not sure if this is the case here, but numerous acquisitions outside of core competencies could point to a strategic shift in positioning, possibly in an effort to shore up declining revenue and relevancy in the core business.