The way I look at this was Diego just wasn't blowing up the league like he did in Germany. Right now our focus is to dominate the league to get top 3. For that we need players that know the league and consistently perform in it. Such as Di Natale, Quag, etc. Diego had some magic moments, a couple of nice assists and a couple goals, thats about it. We need more than that right now and I think the BoD is looking for league proven players that consistently perform.
Aside from the preferred formation, we need someone that fits it better and has already performed well in that formation. It wasn't really far to Diego to be used in a formation that doesn't fit his abilities and I am sure he agreed to move on as a result where he could shine again.