Yes, it must breathe but that is achieved either by venting through the inlet, or to a catch tank. Emission control is why manufacturers feed back into the inlet so that the fumes get burnt. However, GDI engines do not have any fuel in the inlet tract, it’s air only as the fuel is injected straight into the cylinders. This means that the backs of the inlet valves do not get a wash of petrol, only air. So if you introduce crankcase fumes to the inlet tract, over time (50k miles?) carbon can build up excessively on the backs of the valves and seats.
Manufacturers are driven by emission control rather than engine longevity!
