Without a soldermask, how do you mount anything SMD finer than about a SOT-23? (only a slight exaggeration)
I can't imagine mounting even a simple ATTiny, let alone a quad-flat anything or a bunch of 0603s without a solder mask.
I'm sure that some use cases can get by with all DIP, through-hole, and similar-sized parts, but it's hard to design a product that can later scale up cost-effectively without being able to use surface-mount parts. There's a reason the mass production all switched over to SMD->cost.
I can't imagine mounting even a simple ATTiny, let alone a quad-flat anything or a bunch of 0603s without a solder mask.
I'm sure that some use cases can get by with all DIP, through-hole, and similar-sized parts, but it's hard to design a product that can later scale up cost-effectively without being able to use surface-mount parts. There's a reason the mass production all switched over to SMD->cost.