Now, just to be clear, I am talking about standard commercial television. That means American television that is for-profit and ad-supported--basically everything except premium channels like HBO and not-for-profit channels like PBS and C-SPAN.
And also to be clear, I am not taking a position whether this is right or wrong or good or bad. I am simply pointing out that this is how things currently work, and in fact how they have worked since the beginning of American broadcasting.
Now, this is a really basic and important point, because it is pretty much impossible to understand some decisions networks make without knowing this. Ready?
You are not the customer. You are the product.
The network may get a very tiny amount of money from their share of your cable bill, but the overwhelming majority of their money comes from advertisers. But advertisers don't buy ads from networks, they buy them from ad agencies. What they're paying the network for is your attention.
The business of a network is not to make (or, more likely, commission) and transmit shows. That's a stage in the process. The actual business of the network is to sell your attention to advertisers.
So, once again: you are not the customer. You are the product.
The show is not the product. The show is bait.
And that's why Korra got moved to Friday nights and then pulled off the air.