Some players don't have what it takes to play during crunch time. You can be awesome all season long then get scared... It looks like the rest of the Mavericks are making attempts at integrating themselves into the offense, but once they miss a few shots, it's "pass to Dirk" time.
It's not that Dirk has no help, it's just that he is getting no help. There's a difference. The help, the players are there, but they just need to step up.