FB and Zuck have always prioritized a culture of building, and created a place (at least in the early days) where builders could thrive. Over time with massive hiring this obviously changed. If they need to further 'trim the fat' Part of this move could also be as a mechanism for selecting out people who are not comfortable with IC responsibilities as a way to identify people who would not have been a fit for FB in the early days, and thus an attempt to revise at least some of the early culture.