It's a quality of life issue for players. Imagine needing to manually place wires for a complicated circuit setup you are trying to build without bots. Is that fun or just tedious? (Also if I take your example to extremes, is it reasonable that you can carry 10 locomotives, a couple of nuclear ...

I think blue prints place all wires for free (both circuit and power). This is intended behaviour I think.

https://forums.factorio.com/viewtopic.php?t=29014

They should implement that, before they want to release the "finished game" (when that will be). It doesn't make any sense to be like this ...

How to reproduce:
First place and build blueprint "A". Then use blueprint "B" and place it on top of what you made from blueprint "A".
The difference is that blueprint "B" contains circuit network wires.

Result:
When placing blueprint "B" on top of what you made from blueprint "A", the circuit ...