I thought about this already when this was brought first up to me.

But if you think about it you'll notice that this doesn't make a lot of sense:

• There's usually only one output slot in vanilla Minecraft. Loot tables produce multiple stacks
• Recipe books need to know an exact output stack or at least item.
• What would happen if you shift click a recipe to get a whole stack.
• Furnace/brewing recipes work passively couldn't store these items anywhere.
• Loot tables usually need a player context that recipes don't have for good reasons.