I agree with @BigT 's assumption that it’s likely economies of scale. At scale the parts cost between blank and painted is trivial, but the logistics cost for each variant is significant.
Plenty of keyboard variants are completely unavailable even though the difference is just lettering. For example Clear JIS, Clear ISO for FW16 (Clear ISO is available for FW13, but not FW16), and Arabic.
I proposed Combo ANSI/ISO/JIS keyboard layout - #6 by Micah_Lindstrom because it’s one SKU that should work for as many people as possible. Minimizing Framework’s logistics cost should let more people have a keyboard which functions exactly the way they need it.