Since they already own MV Augusta, perhaps they decided Ducati would have been redundant, especially for what is likely limited capital to split between MotoGP efforts, MV Augusta development, and a Ducati purchase and further development.
They may compete with Ducati some day, but without further success on the MotoGP circuit to increase they're name recognition, they'll have to do it with MV, which does have a large (relatively speaking) following.
First post?