Clock direction in MII and RMII Interface

[FreshmanNewbie]

I know that in the MII interface, the clock is always sent from PHY to MAC irrespective of TX or RX? Can someone explain me on why TX and RX, the PHY should send the clocks? Like for the RX connections, since the PHY is sending the RX data to the MAC, the PHY is sending the reference clock. But on the TX lines, the MAC is sending the data to the PHY. In this case, shouldn't the MAC send the clock to the PHY? What's the logic behind this?

Also, when we move to the RMII interface, why there's a change from two clocks to one reference clock? What's the logic behind this move?

Please explain.