I think TakaraTomy had the big box to make it look more "worth it" to people who would buy it in person, or receive it in the mail... as it is a $150-200 toy, so you'd feel like it wasn't worth it if you got a box that was half the size.
Hasbro will probably have some sort of viewing window (if the box looks like a cassette player, the cassette window might be clear), so is likely to have it in robot mode to make it look like better value.