That happens because there was and is no coordination between the agencies/ councils, plus these people don't have proper papers to begin with and they weren't controlled when they entered the country. The latter, BTW, was a deliberate decision by the German head of state.
However, latest images of the Berlin "attack" spawned doubts that it actually was one.
To get to that final position the truck would have had to drive over at least one of the many metal bollards put along that market place. But no bollard nor the front of the truck were damaged. The place without a X-mas market with bollards in roughly 2 m distance from another.
What a lorry looks like after hitting such a bollard:
The route of the truck according to German authorities: The total truck weighs about 40t and is said to have had a speed of 60 km/h (36 mph).
Final position of the truck: Note the bollard right behind the trailer where the truck was supposed to have come from.
The front of the truck without damage to the lower part (and unlike in
Leitmotif
's meme there is also no blood visible):
Except for two victims (of foreign nationality) no names of the German victims have been given.