Please see for demonstration:
Circuit boards were expected to function as identical to the circuits that they contain, but because circuit boards try to create one pin for each external connection, rather than each connected external pin, this is not quite true.
Most importantly, the limit of 7 connections instead of 7 pins is very restrictive. It's very common to have a single output pin outputting to 4 or more places. No circuit board will allow two such instances at once.
But also, it's not possible to distinguish between a group of pins which share an output and other pins which output a completely different kind of signal. For the user of a circuit board, this makes things unclear.