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What happens if you connect the LNB directly to a receiver with only one cable, does the receive[r] control the right and left switching, like the sw21?
Yes. The receiver applies either 13 or 18 volts to its satellite input, depending on what channel it is tuned to. If that input to the receiver is a direct cable from an LNB, then the voltage tells the LNB which polarity to send on that cable.

A single-satellite multiswitch applies a constant 13V to one LNB input and 18V to its other LNB input, effectively "pinning" each cable from the LNB to always carry a particular polarity. In this case, the voltage from the receiver is used to tell the switch which LNB input (i.e., which polarity) to pass through to that receiver.

Also, the receiver selects which satellite (91 degrees or 82 degrees) to listen to by applying or not applying a 22 kHz tone on its satellite input. The voltage plus the tone from the receiver are used to tell a multi-satellite switch (e.g., SW44) which LNB input from which satellite to pass through to that receiver.
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