Because dish and cable still operate in the same way they have for 70 years and a lot of people like it that way. They like that their favorite show comes on at 6pm every Thursday and dish/cable see no reason to offer anything different. It does cost money to create and maintain a system for you to do that and the people who still use dish/cable would most likely not use it.

Unless there have been some changes, dish technology hasn’t changed a lot in 30 years because it costs a lot of money to send up new satellites. For the most part the business for cable hasn’t changed a lot because cable just provides the service not the content.

Streaming on the other hand could do this easily and I think Amazon or Netflix experimented with it but no one really used it.