I don't recall them ever addressing it publicly, but my thought was that they switched because of being able to draft Anderson and Parry. The first 3 years they did run a hybrid front and Chapman was a 2-gap NT whereas Parry has not been. I do think it's interesting they went after Poe, but I think (at least at full health) Poe is one of the rare guys that can play almost any scheme.
So, I wasn't surprised at all by the signing of Al Woods, who is of similar size to Parry. but the reported interest in John Jenkins makes me think that maybe they would like to bring in a 2-gap guy for the right price.