Blueprints in factorio are more often used to automatically build structures with bots than as a guide for the player. You can already automatically build structures with the existing mechanics and even stack multiple in your inventory.
When a blueprint is used as a guide for the player, it usually either removes the tedium of say, counting exactly 24 smelters in a row to fill a belt, or it just gives you a design that you pulled from the internet. Having a feature were people can easily copy designs is not a high priority since it removes a lot of gameplay.
