system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are HD TV channels and regular TV channels separate channels? And why can’t there just be HD channels?
gpt
All older standard definition TVs can't display HD information, but the problem is that some older standard definition TVs can't process HD information.  Since they can't convert HD into something that will fit on their SD screen, they can't show the channel at all.  Telling someone "your TV is too old to use on our fine service" is sure to cost you a customer, and the cost to put out an SD version of the signal is very low.  Since channels are "free" to send out, you spend very little to keep a few customers.