You Asked
Why does my home satellite receiver have to face a specific direction? — Kate, Oakland, Md.

Marshall Answered
It’s because the satellite that is sending the signal to your house is located at a specific point in the sky. If you could take a powerful telescope and point it in the direction that your antenna is pointing, you would be able to actually see the satellite sitting that that point in the sky.

The satellite can sit at a fixed point in the sky because it is in a geosynchronous orbit, as demonstrated here:

The satellite is orbiting at exactly the same rate that the earth is rotating.

An obvious follow-up question is, “well, I don’t have to point my cell phone in any particular direction, so why do I have to aim my satellite antenna at the satellite?” That is because the satellite is about 24,000 miles away, and it doesn’t have a particularly powerful transmitter. So your satellite antenna is a directional antenna. See How does a dish receive a signal from a satellite? for details.