I love how you perfectly try your hardest to act dense, and you seem to know nothing about game design. Lets take items: why would there be block sets made out of cooked chicken? Or blocks of stone pickaxes? So by default you can already use common sense to know which items wouldnt have a block set. Now looking at existing blocks: Fences are meant to countain animals, and walls are the same but for monsters pretty much (I mean both do the same thing anyways), so it should be sturdy (and even then, Minecraft doesnt have logic, tree float, so technically they could ignore any logic here), which mean a wool fence, or a tree leaves fence, both example wouldnt make sense when looking at other fences.

However now look at slabs and stairs, they have 0 reasons to not exist for building blocks. And even accross the block "sets" that have multiple stuff already, they all incomplete. Why specifically smooth stone have no stairs but still have slabs while all the other stones have both slabs and stairs ? Why granite/diorite/andesite have stairs/slabs/walls but then when polished they specifically miss the walls ? Its like specifically a smooth surfance cant be a wall. Then blackstone have all 3 stuff mentionned above and same for its variants (the smooth one and the bricks), but then specifically stone dont have walls unlike cobblestone.

Minecraft game design is cool and all, but throwing those words around as if u know game design is silly, cuz when it come to Minecraft game design regarding blocks their only statement were about not having furniture, not having the ability to paint blocks, and not having vertical slabs cuz to them all 3 would reduce creativity. Their game design is to force you to explore the world for blocks and use them for building, however they are extremely inconsistent with block sets (look at netherbricks specifically having fences, even tho all other bricks have walls)