What are the reasons the Dallas Mavericks lost to the Spurs?

Seriously, I am dumbfounded by their defeat in the playoffs. They've got Boubeois, Kidd, Terry, Barea, Butler for a back court. Haywood and Dampier for big men. And of course former MVP Dirk. This is a FORMIDABLE team. Yet they lost to the Spurs who are losing now to the Suns. It doesn't make any sense.