Why A transceiver with two VFOs can be set to "split" mode, using VFO A for receive and VFO B for transmit. This is standard practice when working DX pileups or stations on repeaters and satellites, where the DX station listens on a different frequency than it transmits on. The radio still transmits and receives one at a time, it just uses a different frequency for each function.
Watch out Full duplex means transmitting and receiving simultaneously, which needs separate transmitter and receiver hardware plus filtering or antennas, not simply a second VFO. And no amateur transceiver transmits on two frequencies at once from one dual-VFO setup.
Dual VFO = split operation: listen here, transmit there. One at a time, just on two different dials.