The bigger question is why does teaching subtraction require a textbook at all? Surely if I asked anyone here to think of six ways to teach a child subtraction, none of the ideas would involve a textbook (or a worksheet).
Wouldn't that make sense? I feel like bad textbooks have given the idea of text books a bad name. And I don't think this is a "no true Scotsman" fallacy. It's more an issue of mostly horrible Scotsman written to align with ridiculous state standards.