Of course it's like that for normal IP applications. But there are management applications/protocols (especially on such a switch) that need to have control over this.
The best example is having a managed switch that provides LLDP neighbour info via snmp. The LLDP implementation runs on the CPU (so the virtual port) but must be able to know the port door RX and control the port for TX.
Of course, without such a protocol, everything can be done in a netif without requiring changes to the current lwip code.