I do not know exactly. The first titles were sold in those clumsy biiig boxes, measuring approximately 19 x 26 cm, that is 7.5 x 10.3 inches! This format had also been used for Atari’s early 400/800 titles. Then they switched to handy small boxes, measuring approximately 14 x 19 cm, that is 5.5 x 7.5 inches. This is the same size they used for most of their 2600, 5200, 7800, XL/XE etc software.

Probably it was just cheaper to produce those smaller boxes …