If you look at the actual array sizes, things will make a lot more sense.
1. The Build Array will add the number of expanded elements to the first dimension. The array size after the first Build Array is (2,0), which is still an empty array.
2. The Transpose Array will swap the array sizes. The array size after the Transpose Array is (0,2), which is still an empty array.
3. Again, the Build Array will add the number of expanded elements to the first dimension. In this case, it will add 1 to the first dimension, resulting in the array size being (1,2), which is no longer an empty array.