The answer is: They have no freedom to move.
However is not completely true, as even in a solid atoms still a move a bit (vibrations).
If atoms were able to slide past each other, then we would have a liquid not a solid. Liquids "flow" but never really "break apart" this is because atoms are sliding between them, think of these as a bucket of marbles rolling down a slope.
If they are free to move in all directions, then you have a gas; that's why someone uses perfume in a room, eventually everyone smells it.