Why LAN Access Points' Roles Change
By default, the device that initiates a connection becomes the master of that connection. So, you might think that for a LAN access point to be master of all its slaves, it just has to make sure that it initiates all the connections. That's fine in theory, but in practice the access point doesn't know which devices want to connect, so it can't initiate the connections.
Instead, the LAN access point allows devices to connect with it, but when it accepts the connection, it accepts on the condition that the connecting device will accept a master-slave switch and become a slave. In that way, we have the best of both worlds: Devices can decide for themselves whether to connect to the LAN access point, but the access point gets to be the master and can efficiently manage its bandwidth.