Several reasons to use arrays instead of collections (or dictionaries):
- you can transfer easily array to range (and vice-versa) with
Range("A1:B12") = MyArray - collections can store only unique keys whereas arrays can store any value
- collections have to store a couple (key, value) whereas you can store whatever in an array
See Chip Pearson’s article about arrays for a better understanding
A better question would rather be why people would use collections over dictionaries (ok, collections are standard VBA whereas you have to import dictionaries)