6 Reasons Marketing Is Moving In-House

3. Continuity has become more important than campaigns. There’s a key difference between funding an ad campaign and supporting a social media effort.

In an ad campaign, you make a pitch, win a deal, execute the creative, provide a report and start over. Agencies are generally funded and organized by campaigns.
But in a socially-oriented world, the connection never stops. You fund, staff, and execute continuously. The traditional agency structure, forged over decades, is not necessarily built for that model.

 https://hbr.org/2015/07/6-reasons-marketing-is-moving-in-house