When Kyle Shanahan came to town, he had seven seasons of experience calling plays at the NFL level and four top ten offenses. When Steve Sarkisian came to town, he had zero years of experience calling an offense at the NFL level. Shanahan was also known, depending on your perspective, as an offensive genius or a very creative coordinator with bad habits. Sark was known as a solid-to-smart play caller at the college level.
In the end, the Falcons decided that experience and familiarity were the keys for this team going forward, and the lesson they learned from the Sark hire was not to take a risk on a relative unknown at the NFL level.