Because I think that he was probably the worst coach you could put in charge of such a talented team and 1990 did hurt.
What happened in 2006 was different. Coach kept Messi on the bench (although I don't think he was that much of an impact player that year) and did not risk as much.
There's a difference between playing totally defensive (i.e. catenaccio) and playing fluid ball control football.
Maradona put a team on the field that couldn't defend against anyone, let alone Germany. Did he really believe he would outscore his way to the World Cup? A good coaches focuses on the strengths and plugs the weaknesses. In this case, he didn't.