The Astro Hog fuselage sides are just printed on balsa sheets. You have to cut them yourself. To switch the kit to use lite ply they'd either have to make dies or do the setup for laser cutting. I have no idea how many Astro Hog kits are sold in a year but I suspect the number is pretty small. Spending any money to change it probably would not make sense.

Some jokes I've seen about building this kit:
Be sure your chainsaw is very sharp before you start.
Have a 55 gallon drum handy to collect all of the wood shavings and sawdust.

I loved my Astro Hog. Lost it due to elevator flutter; at least that's what we think happened. I still have the wing but the fuselage was trashed. My brother has one and I love flying it.